Free Essay

In: Other Topics

Submitted By bdwilson104

Words 206681

Pages 827

Words 206681

Pages 827

rS

al

e

SEVENTH EDITION

DANIEL ANDERSON

University of Iowa

Fo

JEFFERY A. COLE

Anoka-Ramsey Community College

N

ot

DANIEL DRUCKER

Wayne State University

Australia . Brazil . Japan . Korea . Mexico . Singapore . Spain . United Kingdom . United States

ALL RIGHTS RESERVED. No part of this work covered by the copyright herein may be reproduced, transmitted, stored, or used in any form or by any means graphic, electronic, or mechanical, including but not limited to photocopying, recording, scanning, digitizing, taping, Web distribution, information networks, or information storage and retrieval systems, except as permitted under Section 107 or 108 of the 1976 United States

Copyright Act, without the prior written permission of the publisher except as may be permitted by the license terms below. For product information and technology assistance, contact us at

Cengage Learning Customer & Sales Support,

ISBN-13: 978-0-8400-4949-0

ISBN-10: 0-8400-4949-8

Brooks/Cole

20 Davis Drive

Belmont, CA 94002-3098

USA

Cengage Learning is a leading provider of customized learning solutions with office locations around the globe, including Singapore, the United Kingdom, Australia,

Mexico, Brazil, and Japan. Locate your local office at: www.cengage.com/global Cengage Learning products are represented in

Canada by Nelson Education, Ltd.

e

© 2012 Brooks/Cole, Cengage Learning

For your course and learning solutions, visit www.cengage.com/brookscole Purchase any of our products at your local college store or at our preferred online store www.cengagebrain.com

N

ot

Fo

rS

For permission to use material from this text or product, submit all requests online at www.cengage.com/permissions

Further permissions questions can be e-mailed to permissionrequest@cengage.com al

1-800-354-9706

Printed in the United States of America

1 2 3 4 5 6 7 8

15 14 13 12 11

PREFACE

ot

Fo

rS

al

e

This Student Solutions Manual contains strategies for solving and solutions to selected exercises in the text Single Variable Calculus, Seventh Edition, by James Stewart. It contains solutions to the odd-numbered exercises in each section, the review sections, the True-False Quizzes, and the

Problem Solving sections, as well as solutions to all the exercises in the Concept Checks.

This manual is a text supplement and should be read along with the text. You should read all exercise solutions in this manual because many concept explanations are given and then used in subsequent solutions. All concepts necessary to solve a particular problem are not reviewed for every exercise. If you are having difficulty with a previously covered concept, refer back to the section where it was covered for more complete help.

A significant number of today’s students are involved in various outside activities, and find it difficult, if not impossible, to attend all class sessions; this manual should help meet the needs of these students. In addition, it is our hope that this manual’s solutions will enhance the understanding of all readers of the material and provide insights to solving other exercises.

We use some nonstandard notation in order to save space. If you see a symbol that you don’t recognize, refer to the Table of Abbreviations and Symbols on page v.

We appreciate feedback concerning errors, solution correctness or style, and manual style. Any comments may be sent directly to jeff.cole@anokaramsey.edu, or in care of the publisher:

Brooks/Cole, Cengage Learning, 20 Davis Drive, Belmont CA 94002-3098.

We would like to thank Stephanie Kuhns and Kathi Townes, of TECHarts, for their production services; and Elizabeth Neustaetter of Brooks/Cole, Cengage Learning, for her patience and support. All of these people have provided invaluable help in creating this manual.

N

■

Jeffery A. Cole

Anoka-Ramsey Community College

James Stewart

McMaster University and University of Toronto

Daniel Drucker

Wayne State University

Daniel Anderson

University of Iowa

iii

N ot e

al

rS

Fo

ABBREVIATIONS AND SYMBOLS

CD

concave downward

CU

concave upward

D

the domain of f

FDT

First Derivative Test

HA

horizontal asymptote(s)

I

interval of convergence

Increasing/Decreasing Test

IP

inﬂection point(s)

R

radius of convergence

VA

vertical asymptote(s)

CAS

=

indicates the use of a computer algebra system.

H

indicates the use of l’Hospital’s Rule.

j

indicates the use of Formula j in the Table of Integrals in the back endpapers.

s

indicates the use of the substitution {u = sin x, du = cos x dx}.

=

=

c

al

indicates the use of the substitution {u = cos x, du = − sin x dx}.

ot

Fo

=

rS

=

e

I/D

N

■

v

N ot e

al

rS

Fo

CONTENTS

■

1

DIAGNOSTIC TESTS

■

1

FUNCTIONS AND LIMITS

9

1.1

Four Ways to Represent a Function

1.2

Mathematical Models: A Catalog of Essential Functions

1.3

New Functions from Old Functions

1.4

The Tangent and Velocity Problems

1.5

The Limit of a Function

1.6

Calculating Limits Using the Limit Laws

1.7

The Precise Definition of a Limit

1.8

Continuity

e

24

29

34

38

Fo

51

53

DERIVATIVES

ot

■

18

43

Principles of Problem Solving

2

2.1

Derivatives and Rates of Change

2.2

The Derivative as a Function

2.3

Differentiation Formulas

2.4

Derivatives of Trigonometric Functions

2.5

The Chain Rule

2.6

Implicit Differentiation

2.7

Rates of Change in the Natural and Social Sciences

2.8

Related Rates

2.9

Linear Approximations and Differentials

Review

Problems Plus

14

al

26

9

rS

Review

N

■

53

58

64

71

74

79

85

89

94

97

105

vii

CONTENTS

3

■

111

APPLICATIONS OF DIFFERENTIATION

3.1

Maximum and Minimum Values

3.2

The Mean Value Theorem

3.3

How Derivatives Affect the Shape of a Graph

3.4

Limits at Infinity; Horizontal Asymptotes

3.5

Summary of Curve Sketching

3.6

Graphing with Calculus and Calculators

3.7

Optimization Problems

3.8

Newton’s Method

3.9

Antiderivatives

128

135

144

152

162

167

INTEGRALS

189

rS

al

183

4.1

Areas and Distances

189

4.2

The Definite Integral

194

4.3

Fo

■

4.4

4.5

The Fundamental Theorem of Calculus

199

Indeﬁnite Integrals and the Net Change Theorem

The Substitution Rule

Review

Problems Plus

5

■

118

172

Problems Plus

4

116

e

Review

111

208

212

ot

■

217

N

viii

APPLICATIONS OF INTEGRATION

5.1

Areas Between Curves

5.2

Volumes

5.3

Volumes by Cylindrical Shells

5.4

Work

5.5

Average Value of a Function

Review

Problems Plus

219

226

234

238

242

247

241

219

205

CONTENTS

6

■

INVERSE FUNCTIONS:

6.1

Inverse Functions

6.2

Exponential Functions and

Their Derivatives 254

Logarithmic

Functions 261

Derivatives of Logarithmic

Functions 264

6.2*

6.5

Exponential Growth and Decay

286

6.6

Inverse Trigonometric Functions

288

6.7

Hyperbolic Functions

6.8

e

Exponential, Logarithmic, and Inverse Trigonometric Functions

Indeterminate Forms and L’Hospital’s Rule

Review

Problems Plus

■

6.3*

6.4*

294

306

315

7.1

7.2

7.3

Integration by Parts

319

Trigonometric Integrals

Trigonometric Substitution

325

329

Integration of Rational Functions by Partial Fractions

ot

7.4

298

319

TECHNIQUES OF INTEGRATION

Fo

7

The Natural Logarithmic

Function 270

The Natural Exponential

Function 277

General Logarithmic and

Exponential Functions 283

al

6.4

251

rS

6.3

334

Strategy for Integration

7.6

Integration Using Tables and Computer Algebra Systems

7.7

Approximate Integration

7.8

Improper Integrals

N

7.5

Review

343

349

353

361

368

Problems Plus 375

8

■

251

FURTHER APPLICATIONS OF INTEGRATION

8.1

Arc Length

8.2

Area of a Surface of Revolution

8.3

Applications to Physics and Engineering

379

382

386

379

■

ix

CONTENTS

8.4

Applications to Economics and Biology

8.5

Probability

Review

Problems Plus

■

394

401

405

DIFFERENTIAL EQUATIONS

9.1

Modeling with Differential Equations

9.2

Direction Fields and Euler’s Method

9.3

Separable Equations

9.4

Models for Population Growth

9.5

Linear Equations

9.6

Predator-Prey Systems

al

425

433

PARAMETRIC EQUATIONS AND POLAR COORDINATES

Fo

■

417

421

427

Problems Plus

10

406

411

rS

Review

405

e

9

393

397

10.1

Curves Defined by Parametric Equations

10.2

Calculus with Parametric Curves

10.3

Polar Coordinates

ot

■

443

Areas and Lengths in Polar Coordinates

10.5

Conic Sections

10.6

Conic Sections in Polar Coordinates

Review

■

456

462

468

471

Problems Plus

11

437

449

10.4

N

x

479

INFINITE SEQUENCES AND SERIES

11.1

Sequences

11.2

Series

11.3

The Integral Test and Estimates of Sums

11.4

The Comparison Tests

481

481

487

498

495

437

CONTENTS

11.5

Alternating Series

11.6

Absolute Convergence and the Ratio and Root Tests

11.7

Strategy for Testing Series

11.8

Power Series

11.9

Representations of Functions as Power Series

11.10

Taylor and Maclaurin Series

11.11

Applications of Taylor Polynomials

510

519

526

541

547

APPENDIXES

Numbers, Inequalities, and Absolute Values

B

Coordinate Geometry and Lines

C

Graphs of Second-Degree Equations

D

Trigonometry

E

Sigma Notation

G

Graphing Calculators and Computers

547

al

A

549

rS

552

554

558

Fo

Complex Numbers

N

ot

H

514

533

Problems Plus

■

504

508

e

Review

501

564

561

■

xi

N ot e

al

rS

Fo

DIAGNOSTIC TESTS

Test A Algebra

1. (a) (−3)4 = (−3)(−3)(−3)(−3) = 81

(c) 3−4 =

(e)

2 −2

3

1

1

=

34

81

2

= 3 =

2

2. (a) Note that

(b) −34 = −(3)(3)(3)(3) = −81

523

= 523−21 = 52 = 25

521

1

1

1

1

(f ) 16−34 = 34 = √ 3 = 3 =

4

2

8

16

16

(d)

9

4

√

√

√

√

√

√

√

√

√

√

√

200 = 100 · 2 = 10 2 and 32 = 16 · 2 = 4 2. Thus 200 − 32 = 10 2 − 4 2 = 6 2.

332 3

2 −12

−2

=

2 −12

332 3

2

=

(2 −12 )2

4 −1

4

=

= 3 6 = 7

93 6

9

9

(332 3 )2

3. (a) 3( + 6) + 4(2 − 5) = 3 + 18 + 8 − 20 = 11 − 2

al

(c)

e

(b) (33 3 )(42 )2 = 33 3 162 4 = 485 7

(c)

rS

(b) ( + 3)(4 − 5) = 42 − 5 + 12 − 15 = 42 + 7 − 15

√

√ 2

√ √

√ √

√ √ 2 √ √

+

− =

− + −

=−

Fo

Or: Use the formula for the difference of two squares to see that

√

√ √

√ √ 2 √ 2

+

− =

−

= − .

(d) (2 + 3)2 = (2 + 3)(2 + 3) = 42 + 6 + 6 + 9 = 42 + 12 + 9.

Note: A quicker way to expand this binomial is to use the formula ( + )2 = 2 + 2 + 2 with = 2 and = 3:

(2 + 3)2 = (2)2 + 2(2)(3) + 32 = 42 + 12 + 9

ot

(e) See Reference Page 1 for the binomial formula ( + )3 = 3 + 32 + 32 + 3 . Using it, we get

( + 2)3 = 3 + 32 (2) + 3(22 ) + 23 = 3 + 62 + 12 + 8.

N

4. (a) Using the difference of two squares formula, 2 − 2 = ( + )( − ), we have

42 − 25 = (2)2 − 52 = (2 + 5)(2 − 5).

(b) Factoring by trial and error, we get 22 + 5 − 12 = (2 − 3)( + 4).

(c) Using factoring by grouping and the difference of two squares formula, we have

3 − 32 − 4 + 12 = 2 ( − 3) − 4( − 3) = (2 − 4)( − 3) = ( − 2)( + 2)( − 3).

(d) 4 + 27 = (3 + 27) = ( + 3)(2 − 3 + 9)

This last expression was obtained using the sum of two cubes formula, 3 + 3 = ( + )(2 − + 2 ) with =

and = 3. [See Reference Page 1 in the textbook.]

(e) The smallest exponent on is − 1 , so we will factor out −12 .

2

332 − 912 + 6−12 = 3−12 (2 − 3 + 2) = 3−12 ( − 1)( − 2)

(f ) 3 − 4 = (2 − 4) = ( − 2)( + 2) c ° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

1

¤

5. (a)

(b)

(c)

DIAGNOSTIC TESTS

( + 1)( + 2)

+2

2 + 3 + 2

=

=

2 − − 2

( + 1)( − 2)

−2

(2 + 1)( − 1) + 3

−1

22 − − 1 + 3

·

=

·

=

2 − 9

2 + 1

( − 3)( + 3) 2 + 1

−3

2

+1

2

+1

2

+1 −2

2 − ( + 1)( − 2)

−

=

−

=

−

·

=

−4

+2

( − 2)( + 2)

+2

( − 2)( + 2)

+2 −2

( − 2)( + 2)

2

=

2 − (2 − − 2)

+2

1

=

=

( + 2)( − 2)

( + 2)( − 2)

−2

−

−

2 − 2

( − )( + )

+

=

·

=

=

=

= −( + )

(d)

1

1

1

1

−

−( − )

−1

−

−

√

√

√

√

√

√

√

√

√

10

10

5+2

50 + 2 10

5 2 + 2 10

= 5 2 + 2 10

=

= √

·√

= √ 2

2

5−4

5−2

5−2

5+2

5 −2

e

6. (a) √

1

4

1

4

+1−

2

= + 1 +

2

3

4

rS

7. (a) 2 + + 1 = 2 + +

al

√

√

√

4+−2

4+−2

4++2

4+−4

1

= √

= √

= √

=

·√

(b)

4++2

4++2

4++2

4++2

(b) 22 − 12 + 11 = 2(2 − 6) + 11 = 2(2 − 6 + 9 − 9) + 11 = 2(2 − 6 + 9) − 18 + 11 = 2( − 3)2 − 7

(b)

2

2 − 1

=

+1

⇔ + 1 = 14 − 5 ⇔

2

3

2

=9 ⇔ =

2

3

·9 ⇔ =6

Fo

8. (a) + 5 = 14 − 1

2

⇒ 22 = (2 − 1)( + 1) ⇔ 22 = 22 + − 1 ⇔ = 1

(c) 2 − − 12 = 0 ⇔ ( + 3)( − 4) = 0 ⇔ + 3 = 0 or − 4 = 0 ⇔ = −3 or = 4

ot

(d) By the quadratic formula, 22 + 4 + 1 = 0 ⇔

√

√

√

√

2 −2 ± 2

−4 ± 42 − 4(2)(1)

−4 ± 8

−4 ± 2 2

−2 ± 2

=

=

=

=

= −1 ±

=

2(2)

4

4

4

2

1

2

√

2.

N

2

(e) 4 − 32 + 2 = 0 ⇔ (2 − 1)(2 − 2) = 0 ⇔ 2 − 1 = 0 or 2 − 2 = 0 ⇔ 2 = 1 or 2 = 2 ⇔

√

= ±1 or = ± 2

(f ) 3 | − 4| = 10 ⇔ | − 4| =

10

3

⇔ − 4 = − 10 or − 4 =

3

(g) Multiplying through 2(4 − )−12 − 3

⇔ =

2

3

or =

22

3

√

4 − = 0 by (4 − )12 gives 2 − 3(4 − ) = 0 ⇔

2 − 12 + 3 = 0 ⇔ 5 − 12 = 0 ⇔ 5 = 12 ⇔ =

9. (a) −4 5 − 3 ≤ 17

10

3

12

.

5

⇔ −9 −3 ≤ 12 ⇔ 3 ≥ −4 or −4 ≤ 3.

In interval notation, the answer is [−4 3).

(b) 2 2 + 8 ⇔ 2 − 2 − 8 0 ⇔ ( + 2)( − 4) 0. Now, ( + 2)( − 4) will change sign at the critical values = −2 and = 4. Thus the possible intervals of solution are (−∞ −2), (−2 4), and (4 ∞). By choosing a single test value from each interval, we see that (−2 4) is the only interval that satisﬁes the inequality.

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

TEST B ANALYTIC GEOMETRY

¤

3

(c) The inequality ( − 1)( + 2) 0 has critical values of −2 0 and 1. The corresponding possible intervals of solution are (−∞ −2), (−2 0), (0 1) and (1 ∞). By choosing a single test value from each interval, we see that both intervals

(−2 0) and (1 ∞) satisfy the inequality. Thus, the solution is the union of these two intervals: (−2 0) ∪ (1 ∞).

(d) | − 4| 3 ⇔ −3 − 4 3 ⇔ 1 7. In interval notation, the answer is (1 7).

2 − 3

≤1 ⇔

+1

2 − 3

−1 ≤0 ⇔

+1

Now, the expression

−4 may change signs at the critical values = −1 and = 4, so the possible intervals of solution

+1

(e)

2 − 3

+1

−

≤0 ⇔

+1

+1

2 − 3 − − 1

≤0 ⇔

+1

−4

≤ 0.

+1

are (−∞ −1), (−1 4], and [4 ∞). By choosing a single test value from each interval, we see that (−1 4] is the only

interval that satisﬁes the inequality.

10. (a) False. In order for the statement to be true, it must hold for all real numbers, so, to show that the statement is false, pick

e

= 1 and = 2 and observe that (1 + 2)2 6= 12 + 22 . In general, ( + )2 = 2 + 2 + 2 .

√

12 + 22 6= 1 + 2.

rS

(c) False. To see this, let = 1 and = 2, then

al

(b) True as long as and are nonnegative real numbers. To see this, think in terms of the laws of exponents:

√ √

√

= ()12 = 12 12 = .

(d) False. To see this, let = 1 and = 2, then

(f ) True since

1

1

1

6= − .

2−3

2

3

Fo

(e) False. To see this, let = 2 and = 3, then

1 + 1(2)

6= 1 + 1.

2

1

1

· =

, as long as 6= 0 and − 6= 0.

−

−

ot

Test B Analytic Geometry

1. (a) Using the point (2 −5) and = −3 in the point-slope equation of a line, − 1 = ( − 1 ), we get

N

− (−5) = −3( − 2) ⇒ + 5 = −3 + 6 ⇒ = −3 + 1.

(b) A line parallel to the -axis must be horizontal and thus have a slope of 0. Since the line passes through the point (2 −5), the -coordinate of every point on the line is −5, so the equation is = −5.

(c) A line parallel to the -axis is vertical with undeﬁned slope. So the -coordinate of every point on the line is 2 and so the equation is = 2.

(d) Note that 2 − 4 = 3 ⇒ −4 = −2 + 3 ⇒ = 1 − 3 . Thus the slope of the given line is = 1 . Hence, the

2

4

2

slope of the line we’re looking for is also

So the equation of the line is − (−5) =

1

2

(since the line we’re looking for is required to be parallel to the given line).

1

2 (

− 2) ⇒ + 5 = 1 − 1 ⇒ = 1 − 6.

2

2

2. First we’ll ﬁnd the distance between the two given points in order to obtain the radius, , of the circle:

=

√

[3 − (−1)]2 + (−2 − 4)2 = 42 + (−6)2 = 52. Next use the standard equation of a circle,

( − )2 + ( − )2 = 2 , where ( ) is the center, to get ( + 1)2 + ( − 4)2 = 52.

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

¤

DIAGNOSTIC TESTS

3. We must rewrite the equation in standard form in order to identify the center and radius. Note that

2 + 2 − 6 + 10 + 9 = 0 ⇒ 2 − 6 + 9 + 2 + 10 = 0. For the left-hand side of the latter equation, we factor the ﬁrst three terms and complete the square on the last two terms as follows: 2 − 6 + 9 + 2 + 10 = 0 ⇒

( − 3)2 + 2 + 10 + 25 = 25 ⇒ ( − 3)2 + ( + 5)2 = 25. Thus, the center of the circle is (3 −5) and the radius is 5.

4. (a) (−7 4) and (5 −12)

⇒ =

−12 − 4

−16

4

=

=−

5 − (−7)

12

3

(b) − 4 = − 4 [ − (−7)] ⇒ − 4 = − 4 −

3

3

⇒ 3 − 12 = −4 − 28 ⇒ 4 + 3 + 16 = 0. Putting = 0,

28

3

we get 4 + 16 = 0, so the -intercept is −4, and substituting 0 for results in a -intercept of − 16 .

3

(c) The midpoint is obtained by averaging the corresponding coordinates of both points:

−7+5 4+(−12)

2

2

√

√

[5 − (−7)]2 + (−12 − 4)2 = 122 + (−16)2 = 144 + 256 = 400 = 20

= (−1 −4).

e

(d) =

perpendicular bisector passes through (−1 −4) and has slope

3

4

al

(e) The perpendicular bisector is the line that intersects the line segment at a right angle through its midpoint. Thus the

[the slope is obtained by taking the negative reciprocal of

rS

the answer from part (a)]. So the perpendicular bisector is given by + 4 = 3 [ − (−1)] or 3 − 4 = 13.

4

(f ) The center of the required circle is the midpoint of , and the radius is half the length of , which is 10. Thus, the equation is ( + 1)2 + ( + 4)2 = 100.

Fo

5. (a) Graph the corresponding horizontal lines (given by the equations = −1 and

= 3) as solid lines. The inequality ≥ −1 describes the points ( ) that lie on or above the line = −1. The inequality ≤ 3 describes the points ( ) that lie on or below the line = 3. So the pair of inequalities −1 ≤ ≤ 3

ot

describes the points that lie on or between the lines = −1 and = 3.

(b) Note that the given inequalities can be written as −4 4 and −2 2,

N

4

respectively. So the region lies between the vertical lines = −4 and = 4 and between the horizontal lines = −2 and = 2. As shown in the graph, the region common to both graphs is a rectangle (minus its edges) centered at the origin. (c) We ﬁrst graph = 1 − 1 as a dotted line. Since 1 − 1 , the points in the

2

2 region lie below this line.

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

TEST C FUNCTIONS

¤

5

(d) We ﬁrst graph the parabola = 2 − 1 using a solid curve. Since ≥ 2 − 1, the points in the region lie on or above the parabola.

(e) We graph the circle 2 + 2 = 4 using a dotted curve. Since 2 + 2 2, the region consists of points whose distance from the origin is less than 2, that is, the points that lie inside the circle.

(f ) The equation 92 + 16 2 = 144 is an ellipse centered at (0 0). We put it in

2

2

+

= 1. The -intercepts are

16

9

e

standard form by dividing by 144 and get

rS

al

√ located at a distance of 16 = 4 from the center while the -intercepts are a

√

distance of 9 = 3 from the center (see the graph).

Test C Functions

1. (a) Locate −1 on the -axis and then go down to the point on the graph with an -coordinate of −1. The corresponding

Fo

-coordinate is the value of the function at = −1, which is −2. So, (−1) = −2.

(b) Using the same technique as in part (a), we get (2) ≈ 28.

(c) Locate 2 on the -axis and then go left and right to ﬁnd all points on the graph with a -coordinate of 2. The corresponding

ot

-coordinates are the -values we are searching for. So = −3 and = 1.

(d) Using the same technique as in part (c), we get ≈ −25 and ≈ 03.

N

(e) The domain is all the -values for which the graph exists, and the range is all the -values for which the graph exists.

Thus, the domain is [−3 3], and the range is [−2 3].

2. Note that (2 + ) = (2 + )3 and (2) = 23 = 8. So the difference quotient becomes

(2 + )3 − 8

8 + 12 + 62 + 3 − 8

12 + 62 + 3

(12 + 6 + 2 )

(2 + ) − (2)

=

=

=

=

= 12 + 6 + 2 .

3. (a) Set the denominator equal to 0 and solve to ﬁnd restrictions on the domain: 2 + − 2 = 0

⇒

( − 1)( + 2) = 0 ⇒ = 1 or = −2. Thus, the domain is all real numbers except 1 or −2 or, in interval notation, (−∞ −2) ∪ (−2 1) ∪ (1 ∞).

(b) Note that the denominator is always greater than or equal to 1, and the numerator is deﬁned for all real numbers. Thus, the domain is (−∞ ∞).

(c) Note that the function is the sum of two root functions. So is deﬁned on the intersection of the domains of these two root functions. The domain of a square root function is found by setting its radicand greater than or equal to 0. Now, c ° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

¤

DIAGNOSTIC TESTS

4 − ≥ 0 ⇒ ≤ 4 and 2 − 1 ≥ 0 ⇒ ( − 1)( + 1) ≥ 0 ⇒ ≤ −1 or ≥ 1. Thus, the domain of

is (−∞ −1] ∪ [1 4].

4. (a) Reﬂect the graph of about the -axis.

(b) Stretch the graph of vertically by a factor of 2, then shift 1 unit downward.

(c) Shift the graph of right 3 units, then up 2 units.

5. (a) Make a table and then connect the points with a smooth curve:

−2

−1

0

1

2

−8

−1

0

1

8

rS

al

e

(b) Shift the graph from part (a) left 1 unit.

Fo

(c) Shift the graph from part (a) right 2 units and up 3 units.

(d) First plot = 2 . Next, to get the graph of () = 4 − 2 ,

ot

reﬂect about the x-axis and then shift it upward 4 units.

N

6

(e) Make a table and then connect the points with a smooth curve:

0

1

4

9

0

1

2

3

(f ) Stretch the graph from part (e) vertically by a factor of two.

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

TEST D TRIGONOMETRY

¤

(g) First plot = 2 . Next, get the graph of = −2 by reﬂecting the graph of

= 2 about the x-axis.

(h) Note that = 1 + −1 = 1 + 1. So ﬁrst plot = 1 and then shift it upward 1 unit.

6. (a) (−2) = 1 − (−2)2 = −3 and (1) = 2(1) + 1 = 3

e

(b) For ≤ 0 plot () = 1 − 2 and, on the same plane, for 0 plot the graph

rS

al

of () = 2 + 1.

7. (a) ( ◦ )() = (()) = (2 − 3) = (2 − 3)2 + 2(2 − 3) − 1 = 42 − 12 + 9 + 4 − 6 − 1 = 42 − 8 + 2

Fo

(b) ( ◦ )() = ( ()) = (2 + 2 − 1) = 2(2 + 2 − 1) − 3 = 22 + 4 − 2 − 3 = 22 + 4 − 5

(c) ( ◦ ◦ )() = ((())) = ((2 − 3)) = (2(2 − 3) − 3) = (4 − 9) = 2(4 − 9) − 3

= 8 − 18 − 3 = 8 − 21

ot

Test D Trigonometry

300

5

=

=

180◦

180

3

◦

5 180

5

=

= 150◦

2. (a)

6

6

18

=−

=−

180◦

180

10

360◦

180◦

=

≈ 1146◦

(b) 2 = 2

1. (a) 300◦ = 300◦

N

(b) −18◦ = −18◦

3. We will use the arc length formula, = , where is arc length, is the radius of the circle, and is the measure of the

central angle in radians. First, note that 30◦ = 30◦

4. (a) tan(3) =

= . So = (12)

= 2 cm.

◦

180

6

6

√

√

3 You can read the value from a right triangle with sides 1, 2, and 3.

(b) Note that 76 can be thought of as an angle in the third quadrant with reference angle 6. Thus, sin(76) = − 1 ,

2

since the sine function is negative in the third quadrant.

(c) Note that 53 can be thought of as an angle in the fourth quadrant with reference angle 3. Thus, sec(53) =

1

1

=

= 2, since the cosine function is positive in the fourth quadrant. cos(53) 12

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

7

¤

DIAGNOSTIC TESTS

5. sin = 24

6. sin =

1

3

⇒ = 24 sin

and cos = 24 ⇒ = 24 cos

and sin2 + cos2 = 1 ⇒ cos =

So, using the sum identity for the sine, we have

1−

1

9

=

2

√

2

. Also, cos =

3

4

5

⇒ sin =

1−

16

25

√

√

√

2 2 3

4+6 2

1

1 4

· =

=

4+6 2 sin( + ) = sin cos + cos sin = · +

3 5

3

5

15

15

7. (a) tan sin + cos =

2 sin (cos ) sin

2 tan

=

=2 cos2 = 2 sin cos = sin 2

1 + tan2 sec2 cos

8. sin 2 = sin

⇔ 2 sin cos = sin ⇔ 2 sin cos − sin = 0 ⇔ sin (2 cos − 1) = 0 ⇔

sin = 0 or cos =

1

2

⇒ = 0,

,

3

,

5

,

3

2.

e

(b)

sin sin2 cos2

1

sin + cos =

+

=

= sec cos cos cos cos

al

9. We ﬁrst graph = sin 2 (by compressing the graph of sin

ot

Fo

rS

by a factor of 2) and then shift it upward 1 unit.

N

8

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

= 3.

5

1

FUNCTIONS AND LIMITS

1.1 Four Ways to Represent a Function

1. The functions () = +

and are equal.

√

√

2 − and () = + 2 − give exactly the same output values for every input value, so

3. (a) The point (1 3) is on the graph of , so (1) = 3.

(b) When = −1, is about −02, so (−1) ≈ −02.

(c) () = 1 is equivalent to = 1 When = 1, we have = 0 and = 3.

e

(d) A reasonable estimate for when = 0 is = −08.

(e) The domain of consists of all -values on the graph of . For this function, the domain is −2 ≤ ≤ 4, or [−2 4].

al

The range of consists of all -values on the graph of . For this function, the range is −1 ≤ ≤ 3, or [−1 3].

(f ) As increases from −2 to 1, increases from −1 to 3. Thus, is increasing on the interval [−2 1].

rS

5. From Figure 1 in the text, the lowest point occurs at about ( ) = (12 −85). The highest point occurs at about (17 115).

Thus, the range of the vertical ground acceleration is −85 ≤ ≤ 115. Written in interval notation, we get [−85 115]. the Vertical Line Test.

Fo

7. No, the curve is not the graph of a function because a vertical line intersects the curve more than once. Hence, the curve fails

9. Yes, the curve is the graph of a function because it passes the Vertical Line Test. The domain is [−3 2] and the range

is [−3 −2) ∪ [−1 3].

ot

11. The person’s weight increased to about 160 pounds at age 20 and stayed fairly steady for 10 years. The person’s weight

dropped to about 120 pounds for the next 5 years, then increased rapidly to about 170 pounds. The next 30 years saw a gradual

N

increase to 190 pounds. Possible reasons for the drop in weight at 30 years of age: diet, exercise, health problems.

13. The water will cool down almost to freezing as the ice melts. Then, when

the ice has melted, the water will slowly warm up to room temperature.

15. (a) The power consumption at 6 AM is 500 MW which is obtained by reading the value of power when = 6 from the

graph. At 6 PM we read the value of when = 18 obtaining approximately 730 MW

(b) The minimum power consumption is determined by ﬁnding the time for the lowest point on the graph, = 4 or 4 AM. The maximum power consumption corresponds to the highest point on the graph, which occurs just before = 12 or right before noon. These times are reasonable, considering the power consumption schedules of most individuals and businesses. c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

9

10

¤

CHAPTER 1

FUNCTIONS AND LIMITS

17. Of course, this graph depends strongly on the

19. As the price increases, the amount sold

geographical location!

decreases.

21.

(b) From the graph, we estimate the number of US cell-phone

e

23. (a)

al

subscribers to be about 126 million in 2001 and 207 million

25. () = 32 − + 2

Fo

rS

in 2005.

ot

(2) = 3(2)2 − 2 + 2 = 12 − 2 + 2 = 12

(−2) = 3(−2)2 − (−2) + 2 = 12 + 2 + 2 = 16

N

() = 32 − + 2

(−) = 3(−)2 − (−) + 2 = 32 + + 2

( + 1) = 3( + 1)2 − ( + 1) + 2 = 3(2 + 2 + 1) − − 1 + 2 = 32 + 6 + 3 − + 1 = 32 + 5 + 4

2 () = 2 · () = 2(32 − + 2) = 62 − 2 + 4

(2) = 3(2)2 − (2) + 2 = 3(42 ) − 2 + 2 = 122 − 2 + 2

(2 ) = 3(2 )2 − (2 ) + 2 = 3(4 ) − 2 + 2 = 34 − 2 + 2

2

[ ()]2 = 32 − + 2 = 32 − + 2 32 − + 2

= 94 − 33 + 62 − 33 + 2 − 2 + 62 − 2 + 4 = 94 − 63 + 132 − 4 + 4

( + ) = 3( + )2 − ( + ) + 2 = 3(2 + 2 + 2 ) − − + 2 = 32 + 6 + 32 − − + 2

27. () = 4 + 3 − 2 , so (3 + ) = 4 + 3(3 + ) − (3 + )2 = 4 + 9 + 3 − (9 + 6 + 2 ) = 4 − 3 − 2 ,

and

(4 − 3 − 2 ) − 4

(−3 − )

(3 + ) − (3)

=

=

= −3 − .

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

SECTION 1.1

FOUR WAYS TO REPRESENT A FUNCTION

¤

11

1

1

−

−

() − ()

= = − = −1( − ) = − 1

29.

=

−

−

−

( − )

( − )

31. () = ( + 4)(2 − 9) is deﬁned for all except when 0 = 2 − 9

⇔ 0 = ( + 3)( − 3) ⇔ = −3 or 3, so the

domain is { ∈ R | 6= −3 3} = (−∞ −3) ∪ (−3 3) ∪ (3 ∞).

33. () =

√

3

2 − 1 is deﬁned for all real numbers. In fact 3 (), where () is a polynomial, is deﬁned for all real numbers.

Thus, the domain is R or (−∞ ∞).

35. () = 1

√

4

2 − 5 is deﬁned when 2 − 5 0

( − 5) 0. Note that 2 − 5 6= 0 since that would result in

⇔

division by zero. The expression ( − 5) is positive if 0 or 5. (See Appendix A for methods for solving inequalities.) Thus, the domain is (−∞ 0) ∪ (5 ∞).

√

√

√

√

√

2 − is deﬁned when ≥ 0 and 2 − ≥ 0. Since 2 − ≥ 0 ⇒ 2 ≥ ⇒

≤2 ⇒

e

37. () =

al

0 ≤ ≤ 4, the domain is [0 4].

39. () = 2 − 04 is deﬁned for all real numbers, so the domain is R,

rS

or (−∞ ∞) The graph of is a line with slope −04 and -intercept 2.

Fo

41. () = 2 + 2 is deﬁned for all real numbers, so the domain is R, or

(−∞ ∞). The graph of is a parabola opening upward since the coefﬁcient of 2 is positive. To ﬁnd the -intercepts, let = 0 and solve for . 0 = 2 + 2 = (2 + ) ⇒ = 0 or = −2. The -coordinate of

ot

the vertex is halfway between the -intercepts, that is, at = −1. Since

(−1) = 2(−1) + (−1)2 = −2 + 1 = −1, the vertex is (−1 −1).

N

√

− 5 is deﬁned when − 5 ≥ 0 or ≥ 5, so the domain is [5 ∞).

√

Since = − 5 ⇒ 2 = − 5 ⇒ = 2 + 5, we see that is the

43. () =

top half of a parabola.

3 + ||

. Since || =

45. () =

3 +

() =

3 −

−

if ≥ 0 if 0

4

=

2

if 0

if 0

, we have

if 0

=

if 0

4

if 0

2

if 0

Note that is not deﬁned for = 0. The domain is (−∞ 0) ∪ (0 ∞).

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

12

¤

CHAPTER 1

47. () =

FUNCTIONS AND LIMITS

+2

if 0

1−

if ≥ 0

The domain is R.

49. () =

+ 2 if ≤ −1

if −1

2

Note that for = −1, both + 2 and 2 are equal to 1.

The domain is R.

2 − 1 and an equation of the line

2 − 1

e

51. Recall that the slope of a line between the two points (1 1 ) and (2 2 ) is =

al

connecting those two points is − 1 = ( − 1 ). The slope of the line segment joining the points (1 −3) and (5 7) is

53. We need to solve the given equation for .

11

,

2

1 ≤ ≤ 5.

rS

7 − (−3)

5

= , so an equation is − (−3) = 5 ( − 1). The function is () = 5 −

2

2

5−1

2

√

+ ( − 1)2 = 0 ⇔ ( − 1)2 = − ⇔ − 1 = ± − ⇔

√

−. The expression with the positive radical represents the top half of the parabola, and the one with the negative

√

radical represents the bottom half. Hence, we want () = 1 − −. Note that the domain is ≤ 0.

Fo

=1±

55. For 0 ≤ ≤ 3, the graph is the line with slope −1 and -intercept 3, that is, = − + 3. For 3 ≤ 5, the graph is the line

ot

with slope 2 passing through (3 0); that is, − 0 = 2( − 3), or = 2 − 6. So the function is

− + 3 if 0 ≤ ≤ 3

() =

2 − 6 if 3 ≤ 5

N

57. Let the length and width of the rectangle be and . Then the perimeter is 2 + 2 = 20 and the area is = .

Solving the ﬁrst equation for in terms of gives =

20 − 2

= 10 − . Thus, () = (10 − ) = 10 − 2 . Since

2

lengths are positive, the domain of is 0 10. If we further restrict to be larger than , then 5 10 would be the domain.

59. Let the length of a side of the equilateral triangle be . Then by the Pythagorean Theorem, the height of the triangle satisﬁes

√

1 2

= 2 , so that 2 = 2 − 1 2 = 3 2 and = 23 . Using the formula for the area of a triangle,

2

4

4

√ √

= 1 (base)(height), we obtain () = 1 () 23 = 43 2 , with domain 0.

2

2

2 +

61. Let each side of the base of the box have length , and let the height of the box be . Since the volume is 2, we know that

2 = 2 , so that = 22 , and the surface area is = 2 + 4. Thus, () = 2 + 4(22 ) = 2 + (8), with domain 0.

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

SECTION 1.1

FOUR WAYS TO REPRESENT A FUNCTION

¤

13

63. The height of the box is and the length and width are = 20 − 2, = 12 − 2. Then = and so

() = (20 − 2)(12 − 2)() = 4(10 − )(6 − )() = 4(60 − 16 + 2 ) = 43 − 642 + 240.

The sides , , and must be positive. Thus, 0 ⇔ 20 − 2 0 ⇔ 10;

0 ⇔ 12 − 2 0 ⇔ 6; and 0. Combining these restrictions gives us the domain 0 6.

65. We can summarize the amount of the ﬁne with a

piecewise deﬁned function.

15(40 − )

() = 0

15( − 65)

if 0 ≤ 40

if 40 ≤ ≤ 65

if 65

67. (a)

(b) On $14,000, tax is assessed on $4000, and 10%($4000) = $400.

e

On $26,000, tax is assessed on $16,000, and

al

10%($10,000) + 15%($6000) = $1000 + $900 = $1900.

rS

(c) As in part (b), there is $1000 tax assessed on $20,000 of income, so

the graph of is a line segment from (10,000 0) to (20,000 1000).

The tax on $30,000 is $2500, so the graph of for 20,000 is

(30,000 2500).

Fo

the ray with initial point (20,000 1000) that passes through

69. is an odd function because its graph is symmetric about the origin. is an even function because its graph is symmetric with

ot

respect to the -axis.

71. (a) Because an even function is symmetric with respect to the -axis, and the point (5 3) is on the graph of this even function,

N

the point (−5 3) must also be on its graph.

(b) Because an odd function is symmetric with respect to the origin, and the point (5 3) is on the graph of this odd function, the point (−5 −3) must also be on its graph.

73. () =

.

2 + 1

(−) =

−

−

= 2

=− 2

= −().

(−)2 + 1

+1

+1

75. () =

−

, so (−) =

=

.

+1

− + 1

−1

Since this is neither () nor − (), the function is neither even nor odd.

So is an odd function.

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

14

¤

CHAPTER 1 FUNCTIONS AND LIMITS

77. () = 1 + 32 − 4 .

(−) = 1+3(−)2 −(−)4 = 1+32 −4 = ().

So is an even function.

79. (i) If and are both even functions, then (−) = () and (−) = (). Now

( + )(−) = (−) + (−) = () + () = ( + )(), so + is an even function.

(ii) If and are both odd functions, then (−) = − () and (−) = −(). Now

( + )(−) = (−) + (−) = − () + [−()] = −[ () + ()] = −( + )(), so + is an odd function.

e

(iii) If is an even function and is an odd function, then ( + )(−) = (−) + (−) = () + [−()] = () − (), which is not ( + )() nor −( + )(), so + is neither even nor odd. (Exception: if is the zero function, then

1. (a) () = log2 is a logarithmic function.

rS

1.2 Mathematical Models: A Catalog of Essential Functions

al

+ will be odd. If is the zero function, then + will be even.)

√

4

is a root function with = 4.

(c) () =

23 is a rational function because it is a ratio of polynomials.

1 − 2

Fo

(b) () =

(d) () = 1 − 11 + 2542 is a polynomial of degree 2 (also called a quadratic function).

ot

(e) () = 5 is an exponential function.

N

(f ) () = sin cos2 is a trigonometric function.

3. We notice from the ﬁgure that and are even functions (symmetric with respect to the -axis) and that is an odd function

(symmetric with respect to the origin). So (b) = 5 must be . Since is ﬂatter than near the origin, we must have

(c) = 8 matched with and (a) = 2 matched with .

5. (a) An equation for the family of linear functions with slope 2

is = () = 2 + , where is the -intercept.

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

SECTION 1.2 MATHEMATICAL MODELS: A CATALOG OF ESSENTIAL FUNCTIONS

¤

(b) (2) = 1 means that the point (2 1) is on the graph of . We can use the point-slope form of a line to obtain an equation for the family of linear functions through the point (2 1). − 1 = ( − 2), which is equivalent to = + (1 − 2) in slope-intercept form.

(c) To belong to both families, an equation must have slope = 2, so the equation in part (b), = + (1 − 2), becomes = 2 − 3. It is the only function that belongs to both families.

7. All members of the family of linear functions () = − have graphs

rS

al

e

that are lines with slope −1. The -intercept is .

9. Since (−1) = (0) = (2) = 0, has zeros of −1, 0, and 2, so an equation for is () = [ − (−1)]( − 0)( − 2),

or () = ( + 1)( − 2). Because (1) = 6, we’ll substitute 1 for and 6 for ().

Fo

6 = (1)(2)(−1) ⇒ −2 = 6 ⇒ = −3, so an equation for is () = −3( + 1)( − 2).

11. (a) = 200, so = 00417( + 1) = 00417(200)( + 1) = 834 + 834. The slope is 834, which represents the

change in mg of the dosage for a child for each change of 1 year in age.

N

13. (a)

ot

(b) For a newborn, = 0, so = 834 mg.

(b) The slope of

9

5

means that increases

9

5

degrees for each increase

of 1◦ C. (Equivalently, increases by 9 when increases by 5 and decreases by 9 when decreases by 5.) The -intercept of

32 is the Fahrenheit temperature corresponding to a Celsius temperature of 0.

15. (a) Using in place of and in place of , we ﬁnd the slope to be

equation is − 80 = 1 ( − 173) ⇔ − 80 = 1 −

6

6

(b) The slope of

1

6

173

6

10

1

2 − 1

80 − 70

=

= . So a linear

=

2 − 1

173 − 113

60

6

⇔ = 1 + 307 307 = 5116 .

6

6

6

means that the temperature in Fahrenheit degrees increases one-sixth as rapidly as the number of cricket

chirps per minute. Said differently, each increase of 6 cricket chirps per minute corresponds to an increase of 1◦ F.

(c) When = 150, the temperature is given approximately by = 1 (150) +

6

307

6

= 7616 ◦ F ≈ 76 ◦ F.

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

15

16

¤

CHAPTER 1 FUNCTIONS AND LIMITS

17. (a) We are given

434 change in pressure

=

= 0434. Using for pressure and for depth with the point

10 feet change in depth

10

( ) = (0 15), we have the slope-intercept form of the line, = 0434 + 15.

(b) When = 100, then 100 = 0434 + 15 ⇔ 0434 = 85 ⇔ =

85

0434

≈ 19585 feet. Thus, the pressure is

100 lbin2 at a depth of approximately 196 feet.

19. (a) The data appear to be periodic and a sine or cosine function would make the best model. A model of the form

() = cos() + seems appropriate.

(b) The data appear to be decreasing in a linear fashion. A model of the form () = + seems appropriate.

Exercises 21 – 24: Some values are given to many decimal places. These are the results given by several computer algebra systems — rounding is left to the reader.

e

(b) Using the points (4000 141) and (60,000 82), we obtain

21. (a)

rS

Fo

A linear model does seem appropriate.

al

82 − 141

( − 4000) or, equivalently,

60,000 − 4000

≈ −0000105357 + 14521429.

− 141 =

(c) Using a computing device, we obtain the least squares regression line = −00000997855 + 13950764.

The following commands and screens illustrate how to ﬁnd the least squares regression line on a TI-84 Plus. to enter the editor.

N

ot

Enter the data into list one (L1) and list two (L2). Press

Find the regession line and store it in Y1 . Press

.

Note from the last ﬁgure that the regression line has been stored in Y1 and that Plot1 has been turned on (Plot1 is

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

SECTION 1.2 MATHEMATICAL MODELS: A CATALOG OF ESSENTIAL FUNCTIONS

highlighted). You can turn on Plot1 from the Y= menu by placing the cursor on Plot1 and pressing

¤

17

or by

.

pressing

Now press

to produce a graph of the data and the regression

line. Note that choice 9 of the ZOOM menu automatically selects a window

(d) When = 25,000, ≈ 11456; or about 115 per 100 population.

(e) When = 80,000, ≈ 5968; or about a 6% chance.

23. (a) A linear model seems appropriate over the time interval

ot

Fo

rS

considered.

al

(f ) When = 200,000, is negative, so the model does not apply.

e

that displays all of the data.

(b) Using a computing device, we obtain the regression line ≈ 00265 − 468759. It is plotted in the graph in part (a).

N

(c) For = 2008, the linear model predicts a winning height of 6.27 m, considerably higher than the actual winning height of 5.96 m.

(d) It is not reasonable to use the model to predict the winning height at the 2100 Olympics since 2100 is too far from the

1896–2004 range on which the model is based.

25. If is the original distance from the source, then the illumination is () = −2 = 2 . Moving halfway to the lamp gives

us an illumination of

−2

1

= 1

= (2)2 = 4(2 ), so the light is 4 times as bright.

2

2

27. (a) Using a computing device, we obtain a power function = , where ≈ 31046 and ≈ 0308.

(b) If = 291, then = ≈ 178, so you would expect to ﬁnd 18 species of reptiles and amphibians on Dominica.

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

18

¤

CHAPTER 1 FUNCTIONS AND LIMITS

1.3 New Functions from Old Functions

1. (a) If the graph of is shifted 3 units upward, its equation becomes = () + 3.

(b) If the graph of is shifted 3 units downward, its equation becomes = () − 3.

(c) If the graph of is shifted 3 units to the right, its equation becomes = ( − 3).

(d) If the graph of is shifted 3 units to the left, its equation becomes = ( + 3).

(e) If the graph of is reﬂected about the -axis, its equation becomes = − ().

(f ) If the graph of is reﬂected about the -axis, its equation becomes = (−).

(g) If the graph of is stretched vertically by a factor of 3, its equation becomes = 3 ().

(h) If the graph of is shrunk vertically by a factor of 3, its equation becomes = 1 ().

3

e

3. (a) (graph 3) The graph of is shifted 4 units to the right and has equation = ( − 4).

al

(b) (graph 1) The graph of is shifted 3 units upward and has equation = () + 3.

(c) (graph 4) The graph of is shrunk vertically by a factor of 3 and has equation = 1 ().

3

rS

(d) (graph 5) The graph of is shifted 4 units to the left and reﬂected about the -axis. Its equation is = − ( + 4).

(e) (graph 2) The graph of is shifted 6 units to the left and stretched vertically by a factor of 2. Its equation is

= 2 ( + 6).

ot

horizontally by a factor of 2.

N

The point (4 −1) on the graph of corresponds to the

point 1 · 4 −1 = (2 −1).

2

(c) To graph = (−) we reﬂect the graph of about the -axis.

The point (4 −1) on the graph of corresponds to the point (−1 · 4 −1) = (−4 −1).

(b) To graph =

Fo

5. (a) To graph = (2) we shrink the graph of

1

we stretch the graph of

2

horizontally by a factor of 2.

The point (4 −1) on the graph of corresponds to the

point (2 · 4 −1) = (8 −1).

(d) To graph = − (−) we reﬂect the graph of about the -axis, then about the -axis.

The point (4 −1) on the graph of corresponds to the

point (−1 · 4 −1 · −1) = (−4 1).

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

SECTION 1.3 NEW FUNCTIONS FROM OLD FUNCTIONS

7. The graph of = () =

¤

√

3 − 2 has been shifted 4 units to the left, reﬂected about the -axis, and shifted downward

1 unit. Thus, a function describing the graph is

=

−1 ·

reﬂect about -axis

( + 4)

shift 4 units left

− 1

shift 1 unit left

This function can be written as

√

= − ( + 4) − 1 = − 3( + 4) − ( + 4)2 − 1 = − 3 + 12 − (2 + 8 + 16) − 1 = − −2 − 5 − 4 − 1

1

: Start with the graph of the reciprocal function = 1 and shift 2 units to the left.

+2

√

√

3

and reﬂect about the -axis.

√

√

− 2 − 1: Start with the graph of = , shift 2 units to the right, and then shift 1 unit downward.

N

13. =

ot

Fo

11. = − 3 : Start with the graph of =

rS

al

e

9. =

15. = sin(2): Start with the graph of = sin and stretch horizontally by a factor of 2.

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

19

20

¤

17. =

CHAPTER 1 FUNCTIONS AND LIMITS

1

2 (1

− cos ): Start with the graph of = cos , reﬂect about the -axis, shift 1 unit upward, and then shrink vertically by

a factor of 2.

19. = 1 − 2 − 2 = −(2 + 2) + 1 = −(2 + 2 + 1) + 2 = −( + 1)2 + 2: Start with the graph of = 2 , reﬂect about

rS

al

e

the -axis, shift 1 unit to the left, and then shift 2 units upward.

√

ot

Fo

21. = | − 2|: Start with the graph of = || and shift 2 units to the right.

N

23. = | − 1|: Start with the graph of =

√

, shift it 1 unit downward, and then reﬂect the portion of the graph below the

-axis about the -axis.

25. This is just like the solution to Example 4 except the amplitude of the curve (the 30◦ N curve in Figure 9 on June 21) is

2

14 − 12 = 2. So the function is () = 12 + 2 sin 365 ( − 80) . March 31 is the 90th day of the year, so the model gives

(90) ≈ 1234 h. The daylight time (5:51 AM to 6:18 PM) is 12 hours and 27 minutes, or 1245 h. The model value differs from the actual value by

1245−1234

1245

≈ 0009, less than 1%.

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

SECTION 1.3 NEW FUNCTIONS FROM OLD FUNCTIONS

¤

27. (a) To obtain = (||), the portion of the graph of = () to the right of the -axis is reﬂected about the -axis.

(c) =

(b) = sin ||

29. () = 3 + 22 ; () = 32 − 1.

||

= R for both and .

(a) ( + )() = (3 + 22 ) + (32 − 1) = 3 + 52 − 1, = R.

(b) ( − )() = (3 + 22 ) − (32 − 1) = 3 − 2 + 1, = R.

e

(c) ( )() = (3 + 22 )(32 − 1) = 35 + 64 − 3 − 22 , = R.

31. () = 2 − 1, = R;

() = 2 + 1, = R.

al

3 + 22

1

since 32 − 1 6= 0.

() =

, = | 6= ± √

(d)

32 − 1

3

rS

(a) ( ◦ )() = (()) = (2 + 1) = (2 + 1)2 − 1 = (42 + 4 + 1) − 1 = 42 + 4, = R.

(b) ( ◦ )() = ( ()) = (2 − 1) = 2(2 − 1) + 1 = (22 − 2) + 1 = 22 − 1, = R.

Fo

(c) ( ◦ )() = ( ()) = (2 − 1) = (2 − 1)2 − 1 = (4 − 22 + 1) − 1 = 4 − 22 , = R.

(d) ( ◦ )() = (()) = (2 + 1) = 2(2 + 1) + 1 = (4 + 2) + 1 = 4 + 3, = R.

33. () = 1 − 3; () = cos .

= R for both and , and hence for their composites.

ot

(a) ( ◦ )() = (()) = (cos ) = 1 − 3 cos .

(b) ( ◦ )() = ( ()) = (1 − 3) = cos(1 − 3).

N

(c) ( ◦ )() = ( ()) = (1 − 3) = 1 − 3(1 − 3) = 1 − 3 + 9 = 9 − 2.

(d) ( ◦ )() = (()) = (cos ) = cos(cos ) [Note that this is not cos · cos .]

+1

1

, = { | 6= 0}; () =

, = { | 6= −2}

+2

+1

+1

1

+2

+1

=

=

+

+

(a) ( ◦ )() = (()) =

+1

+2

+2

+2

+1

+2

2

+ 2 + 1 + 2 + 4 + 4

22 + 6 + 5

( + 1)( + 1) + ( + 2)( + 2)

=

=

=

( + 2)( + 1)

( + 2)( + 1)

( + 2)( + 1)

35. () = +

Since () is not deﬁned for = −2 and (()) is not deﬁned for = −2 and = −1, the domain of ( ◦ )() is = { | 6= −2 −1}.

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

21

22

¤

CHAPTER 1 FUNCTIONS AND LIMITS

1

2 + 1 +

+

+1

2 + + 1

2 + + 1

1

=

=

= 2

(b) ( ◦ )() = ( ()) = +

= 2

+ 2 + 1

( + 1)2

1

+ 1 + 2

+

+2

Since () is not deﬁned for = 0 and ( ()) is not deﬁned for = −1, the domain of ( ◦ )() is = { | 6= −1 0}.

1

1

1

1

1

1

= +

+

+ 2

=+ + 2

(c) ( ◦ )() = ( ()) = +

1 = +

+1

+1

+

2

2

4

2

2

() + 1 + 1 + 1 + ()

+ + + 1 + 2

=

=

2 + 1)

(

(2 + 1)

= { | 6= 0}

+1

(d) ( ◦ )() = (()) =

+2

e

4 + 32 + 1

(2 + 1)

+1

+ 1 + 1( + 2)

+1

2 + 3

+1++2

+2

+2

=

=

=

=

+1

+ 1 + 2( + 2)

+ 1 + 2 + 4

3 + 5

+2

+2

+2

al

=

rS

Since () is not deﬁned for = −2 and (()) is not deﬁned for = − 5 ,

3

the domain of ( ◦ )() is = | 6= −2 − 5 .

3

Fo

37. ( ◦ ◦ )() = ((())) = ((2 )) = (sin(2 )) = 3 sin(2 ) − 2

39. ( ◦ ◦ )() = ((())) = ((3 + 2)) = [(3 + 2)2 ]

= (6 + 43 + 4) =

√

(6 + 43 + 4) − 3 = 6 + 43 + 1

√

3

and () =

√

3

√

√ = ().

. Then ( ◦ )() = (()) = ( 3 ) =

1+

1+ 3

N

43. Let () =

ot

41. Let () = 2 + 2 and () = 4 . Then ( ◦ )() = (()) = (2 + 2 ) = (2 + 2 )4 = ().

45. Let () = 2 and () = sec tan . Then ( ◦ )() = (()) = (2 ) = sec(2 ) tan(2 ) = ().

47. Let () =

√

√

, () = − 1, and () = . Then

√

√

√

( ◦ ◦ )() = ((())) = (( )) = ( − 1) =

− 1 = ().

49. Let () =

√

, () = sec , and () = 4 . Then

√

√

√ 4

√

( ◦ ◦ )() = ((())) = (( )) = (sec ) = (sec ) = sec4 ( ) = ().

51. (a) (2) = 5, because the point (2 5) is on the graph of . Thus, ((2)) = (5) = 4, because the point (5 4) is on the

graph of .

(b) ((0)) = (0) = 3

(c) ( ◦ )(0) = ((0)) = (3) = 0 c ° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

SECTION 1.3 NEW FUNCTIONS FROM OLD FUNCTIONS

¤

(d) ( ◦ )(6) = ( (6)) = (6). This value is not deﬁned, because there is no point on the graph of that has

-coordinate 6.

(e) ( ◦ )(−2) = ((−2)) = (1) = 4

(f ) ( ◦ )(4) = ( (4)) = (2) = −2

53. (a) Using the relationship distance = rate · time with the radius as the distance, we have () = 60.

(b) = 2

⇒ ( ◦ )() = (()) = (60)2 = 36002 . This formula gives us the extent of the rippled area

(in cm2 ) at any time .

55. (a) From the ﬁgure, we have a right triangle with legs 6 and , and hypotenuse .

By the Pythagorean Theorem, 2 + 62 = 2

⇒ = () =

√

2 + 36.

(b) Using = , we get = (30 kmh)( hours) = 30 (in km). Thus,

√

(30)2 + 36 = 9002 + 36. This function represents the distance between the

al

(c) ( ◦ )() = (()) = (30) =

e

= () = 30.

lighthouse and the ship as a function of the time elapsed since noon.

(b)

0

if 0

1

if ≥ 0

Fo

() =

rS

57. (a)

() =

0

if 0

120 if ≥ 0

so () = 120().

Starting with the formula in part (b), we replace 120 with 240 to reﬂect the

(c)

different voltage. Also, because we are starting 5 units to the right of = 0,

ot

we replace with − 5. Thus, the formula is () = 240( − 5).

N

59. If () = 1 + 1 and () = 2 + 2 , then

( ◦ )() = (()) = (2 + 2 ) = 1 (2 + 2 ) + 1 = 1 2 + 1 2 + 1 .

So ◦ is a linear function with slope 1 2 .

61. (a) By examining the variable terms in and , we deduce that we must square to get the terms 42 and 4 in . If we let

() = 2 + , then ( ◦ )() = (()) = (2 + 1) = (2 + 1)2 + = 42 + 4 + (1 + ). Since

() = 42 + 4 + 7, we must have 1 + = 7. So = 6 and () = 2 + 6.

(b) We need a function so that (()) = 3(()) + 5 = (). But

() = 32 + 3 + 2 = 3(2 + ) + 2 = 3(2 + − 1) + 5, so we see that () = 2 + − 1.

63. We need to examine (−).

(−) = ( ◦ )(−) = ((−)) = (()) [because is even]

= ()

Because (−) = (), is an even function. c ° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

23

24

¤

CHAPTER 1

FUNCTIONS AND LIMITS

1.4 The Tangent and Velocity Problems

1. (a) Using (15 250), we construct the following table:

(b) Using the values of that correspond to the points closest to ( = 10 and = 20), we have

slope =

5

(5 694)

694−250

5−15

= − 444 = −444

10

10

(10 444)

444−250

10−15

= − 194 = −388

5

20

(20 111)

111−250

20−15

= − 139 = −278

5

25

(25 28)

28−250

25−15

30

(30 0)

0−250

30−15

−388 + (−278)

= −333

2

= − 222 = −222

10

= − 250 = −166

15

−300

9

= −333.

1

, (2 −1)

1−

(i)

15

(ii)

19

(iii)

199

(iv)

1999

(v)

25

(b) The slope appears to be 1.

(c) Using = 1, an equation of the tangent line to the

( 1(1 − ))

(15 −2)

2

(199 −1010 101)

(19 −1111 111)

1111 111

(1999 −1001 001)

21

201

(21 −0909 091)

(viii)

2001

0909 091

(2001 −0999 001)

= − 3.

1001 001

0999 001

N

(vi)

(vii)

curve at (2 −1) is − (−1) = 1( − 2), or

1010 101

ot

3. (a) =

Fo

rS

al

tangent line at to be

e

(c) From the graph, we can estimate the slope of the

(25 −0666 667)

0666 667

(201 −0990 099)

0990 099

5. (a) = () = 40 − 162 . At = 2, = 40(2) − 16(2)2 = 16. The average velocity between times 2 and 2 + is

ave

40(2 + ) − 16(2 + )2 − 16

(2 + ) − (2)

−24 − 162

=

=

=

= −24 − 16, if 6= 0.

(2 + ) − 2

(i) [2 25]: = 05, ave = −32 fts

(iii) [2 205]: = 005, ave = −248 fts

(ii) [2 21]: = 01, ave = −256 fts

(iv) [2 201]: = 001, ave = −2416 fts

(b) The instantaneous velocity when = 2 ( approaches 0) is −24 fts. c ° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

SECTION 1.4

7. (a) (i) On the interval [1 3], ave =

THE TANGENT AND VELOCITY PROBLEMS

¤

(3) − (1)

107 − 14

93

=

=

= 465 ms.

3−1

2

2

(ii) On the interval [2 3], ave =

(3) − (2)

107 − 51

=

= 56 ms.

3−2

1

(iii) On the interval [3 5], ave =

258 − 107

151

(5) − (3)

=

=

= 755 ms.

5−3

2

2

(iv) On the interval [3 4], ave =

177 − 107

(4) − (3)

=

= 7 ms.

4−3

1

(b)

Using the points (2 4) and (5 23) from the approximate tangent

23 − 4

≈ 63 ms.

5−2

rS

al

e

line, the instantaneous velocity at = 3 is about

9. (a) For the curve = sin(10) and the point (1 0):

(2 0)

15

(15 08660)

14

(14 −04339)

13

12

(13 −08230)

(12 08660)

(11 −02817)

0

05

(05 0)

17321

06

(06 08660)

−10847

07

(07 07818)

08

(08 1)

43301

09

(09 −03420)

−27433

−28173

ot

11

Fo

2

0

−21651

−26061

−5

34202

(b)

N

As approaches 1, the slopes do not appear to be approaching any particular value.

We see that problems with estimation are caused by the frequent oscillations of the graph. The tangent is so steep at that we need to take -values much closer to 1 in order to get accurate estimates of its slope.

(c) If we choose = 1001, then the point is (1001 −00314) and ≈ −313794. If = 0999, then is

(0999 00314) and = −314422. The average of these slopes is −314108. So we estimate that the slope of the tangent line at is about −314.

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

25

26

¤

CHAPTER 1

FUNCTIONS AND LIMITS

1.5 The Limit of a Function

1. As approaches 2, () approaches 5. [Or, the values of () can be made as close to 5 as we like by taking sufﬁciently

close to 2 (but 6= 2).] Yes, the graph could have a hole at (2 5) and be deﬁned such that (2) = 3.

3. (a) lim () = ∞ means that the values of () can be made arbitrarily large (as large as we please) by taking

→−3

sufﬁciently close to −3 (but not equal to −3).

(b) lim () = −∞ means that the values of () can be made arbitrarily large negative by taking sufﬁciently close to 4

→4+

through values larger than 4.

5. (a) As approaches 1, the values of () approach 2, so lim () = 2.

→1

(b) As approaches 3 from the left, the values of () approach 1, so lim () = 1.

→3−

→3+

e

(c) As approaches 3 from the right, the values of () approach 4, so lim () = 4.

(d) lim () does not exist since the left-hand limit does not equal the right-hand limit.

al

→3

(e) When = 3, = 3, so (3) = 3.

(b) lim () = −2

rS

7. (a) lim () = −1

→0−

→0+

(c) lim () does not exist because the limits in part (a) and part (b) are not equal.

→0

(d) lim () = 2

(e) lim () = 0

→2−

→2+

Fo

(f ) lim () does not exist because the limits in part (d) and part (e) are not equal.

→2

(g) (2) = 1

(h) lim () = 3

→4

9. (a) lim () = −∞

(b) lim () = ∞

(d) lim () = −∞

→6−

→−3

(c) lim () = ∞

→0

(e) lim () = ∞

ot

→−7

→6+

N

(f ) The equations of the vertical asymptotes are = −7, = −3, = 0, and = 6.

11. From the graph of

1 + if −1

if −1 ≤ 1 ,

() = 2

2 − if ≥ 1

we see that lim () exists for all except = −1. Notice that the

→

right and left limits are different at = −1.

13. (a) lim () = 1

→0−

(b) lim () = 0

→0+

(c) lim () does not exist because the limits in

→0

part (a) and part (b) are not equal. c ° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

SECTION 1.5

15. lim () = −1,

→0−

17. lim () = 4,

lim () = 2, (0) = 1

→0+

THE LIMIT OF A FUNCTION

lim () = 2, lim () = 2,

→−2

→3−

→3+

(3) = 3, (−2) = 1

2 − 2

:

−−2

21. For () =

2

()

()

19

21

0677419

195

0661017

205

0672131

199

0665552

201

0667774

1995

0666110

2005

2001

0667221

0666778

1999

0655172

0666556

2

→2

√

+4−2

:

()

0236068

05

0242641

01

0248457

005

0249224

001

0249844

N

1

It appears that lim

→0

−1

()

0329033

±05

0458209

±01

0498333

±001

0499983

±02

→0

25. For () =

()

0493331

±005

It appears that lim

ot

23. For () =

− 2

= 0¯ = 2 .

6 3

2 − − 2

Fo

It appears that lim

±1

al

0714286

rS

25

sin

:

+ tan

e

19. For () =

0499583

sin

1

= 05 = .

+ tan

2

6 − 1

:

10 − 1

()

()

0267949

05

0985337

15

0183369

−05

0258343

09

0719397

11

0484119

−01

0251582

095

0660186

105

0540783

−005

0250786

099

0612018

101

0588022

−001

0250156

0999

0601200

1001

0598800

√

+4−2

= 025 = 1 .

4

27. (a) From the graphs, it seems that lim

→0

cos 2 − cos

= −15.

2

It appears that lim

→1

6 − 1

= 06 = 3 .

5

10 − 1

(b)

()

±01

−1493759

±0001

−1499999

±001

±00001

−1499938

−1500000

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

¤

27

28

29.

¤

CHAPTER 1

lim

→−3+

31. lim

→1

33.

35.

FUNCTIONS AND LIMITS

+2

= −∞ since the numerator is negative and the denominator approaches 0 from the positive side as → −3+ .

+3

2−

= ∞ since the numerator is positive and the denominator approaches 0 through positive values as → 1.

( − 1)2

lim

→−2+

−1

−1

= −∞ since ( + 2) → 0 as → −2+ and 2

0 for −2 0.

2 ( + 2)

( + 2)

lim csc = lim

→2 −

→2 −

= −∞ since the numerator is positive and the denominator approaches 0 through negative sin

values as → 2− .

37. lim

→2+

2 − 2 − 8

( − 4)( + 2)

= lim

= ∞ since the numerator is negative and the denominator approaches 0 through

2 − 5 + 6 →2+ ( − 3)( − 2)

1

.

3 − 1

05

From these calculations, it seems that

→1−

→1+

−114

09

099

−369

0999

09999

099999

()

15

042

11

302

−337

101

330

−3337

1001

3330

−33337

10001

33330

−33,3337

100001

33,3333

rS

lim () = −∞ and lim () = ∞.

()

al

39. (a) () =

e

negative values as → 2+ .

Fo

(b) If is slightly smaller than 1, then 3 − 1 will be a negative number close to 0, and the reciprocal of 3 − 1, that is, (), will be a negative number with large absolute value. So lim () = −∞.

→1−

If is slightly larger than 1, then − 1 will be a small positive number, and its reciprocal, (), will be a large positive

3

→1+

ot

number. So lim () = ∞.

(c) It appears from the graph of that

N

lim () = −∞ and lim () = ∞.

→1−

→1+

41. For () = 2 − (21000):

(a)

(b)

()

()

1

08

06

04

02

01

0998000

0638259

0358484

0158680

0038851

0008928

004

002

001

0005

0003

0000572

−0000614

−0000907

−0000978

−0000993

005

0001465

It appears that lim () = 0.

0001

−0001000

It appears that lim () = −0001.

→0

→0

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

SECTION 1.6

CALCULATING LIMITS USING THE LIMIT LAWS

¤

29

43. No matter how many times we zoom in toward the origin, the graphs of () = sin() appear to consist of almost-vertical

al

e

lines. This indicates more and more frequent oscillations as → 0.

There appear to be vertical asymptotes of the curve = tan(2 sin ) at ≈ ±090

45.

rS

and ≈ ±224. To ﬁnd the exact equations of these asymptotes, we note that the graph of the tangent function has vertical asymptotes at = must have 2 sin =

2

+ , or equivalently, sin =

4

2

+ . Thus, we

+ . Since

2

4

(corresponding

Fo

−1 ≤ sin ≤ 1, we must have sin = ± and so = ± sin−1

4

to ≈ ±090). Just as 150◦ is the reference angle for 30◦ , − sin−1 is the

4

−1

−1 reference angle for sin 4 . So = ± − sin 4 are also equations of

ot

vertical asymptotes (corresponding to ≈ ±224).

N

1.6 Calculating Limits Using the Limit Laws

1. (a) lim [ () + 5()] = lim () + lim [5()]

→2

→2

→2

= lim () + 5 lim ()

→2

→2

[Limit Law 1]

(b) lim [()]3 =

→2

[Limit Law 3]

3 lim ()

→2

[Limit Law 6]

= ( −2)3 = −8

= 4 + 5(−2) = −6

(c) lim

→2

() = lim ()

→2

=

[Limit Law 11]

(d) lim

→2

lim [3 ()]

3 ()

→2

=

()

lim ()

[Limit Law 5]

→2

√

4=2

3 lim ()

=

→2

lim ()

[Limit Law 3]

→2

=

3(4)

= −6

−2

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

30

¤

CHAPTER 1

FUNCTIONS AND LIMITS

(e) Because the limit of the denominator is 0, we can’t use Limit Law 5. The given limit, lim

→2

()

, does not exist because the

()

denominator approaches 0 while the numerator approaches a nonzero number.

(f) lim

→2

lim [() ()]

() ()

→2

=

() lim ()

[Limit Law 5]

→2

=

lim () · lim ()

→2

→2

[Limit Law 4]

lim ()

→2

=

−2 · 0

=0

4

[Limit Laws 2 and 1]

3. lim (53 − 32 + − 6) = lim (53 ) − lim (32 ) + lim − lim 6

→3

→3

→3

→3

→3

= 5 lim 3 − 3 lim 2 + lim − lim 6

[3]

= 5(33 ) − 3(32 ) + 3 − 6

[9, 8, and 7]

→3

→3

→3

e

→3

al

= 105 lim (4 − 2)

4 − 2

→−2

=

5. lim

→−2 22 − 3 + 2 lim (22 − 3 + 2)

=

lim 4 − lim 2

→−2

2 lim 2 −

→−2

→−2

3 lim + lim 2

→−2

=

→8

14

7

=

16

8

[9, 7, and 8]

√

√

3

) (2 − 62 + 3 ) = lim (1 + 3 ) · lim (2 − 62 + 3 )

ot

7. lim (1 +

16 − 2

2(4) − 3(−2) + 2

[1, 2, and 3]

Fo

=

→−2

rS

[Limit Law 5]

→−2

→8

=

lim 1 + lim

→8

[Limit Law 4]

→8

→8

√

3

· lim 2 − 6 lim 2 + lim 3

→8

N

√

= 1 + 3 8 · 2 − 6 · 82 + 83

→8

→8

[1, 2, and 3]

[7, 10, 9]

= (3)(130) = 390

9. lim

→2

22 + 1

=

3 − 2

22 + 1

→2 3 − 2

lim (22 + 1)

→2

=

lim (3 − 2)

[Limit Law 11]

lim

[5]

→2

2 lim 2 + lim 1

→2

→2

=

3 lim − lim 2

[1, 2, and 3]

2(2)2 + 1

=

3(2) − 2

[9, 8, and 7]

→2

=

→2

9

3

=

4

2

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

SECTION 1.6

CALCULATING LIMITS USING THE LIMIT LAWS

11. lim

2 − 6 + 5

( − 5)( − 1)

= lim

= lim ( − 1) = 5 − 1 = 4

→5

→5

−5

−5

13. lim

¤

2 − 5 + 6 does not exist since − 5 → 0, but 2 − 5 + 6 → 6 as → 5.

−5

→5

→5

15. lim

→−3

2 − 9

( + 3)( − 3)

−3

−3 − 3

−6

6

= lim

= lim

=

=

=

22 + 7 + 3 →−3 (2 + 1)( + 3) →−3 2 + 1

2(−3) + 1

−5

5

(−5 + )2 − 25

(25 − 10 + 2 ) − 25

−10 + 2

(−10 + )

= lim

= lim

= lim

= lim (−10 + ) = −10

→0

→0

→0

→0

17. lim

→0

19. By the formula for the sum of cubes, we have

lim

→−2

+2

+2

1

1

1

= lim

= lim

=

=

.

3 + 8 →−2 ( + 2)(2 − 2 + 4) →−2 2 − 2 + 4

4+4+4

12

→0

1

1

1

√

= lim √

=

=

→0

3+3

6

9++3

9++3

al

= lim

e

√

2

√

√

√

9 + − 32

9+−3

9+−3

9++3

(9 + ) − 9

= lim √

21. lim

= lim √

= lim

·√

→0

→0

→0

9 + + 3 →0 9 + + 3

9++3

rS

1

+4

1

+

+4

1

1

1

4

= lim 4 = lim

23. lim

= lim

=

=−

→−4 4 +

→−4 4 +

→−4 4(4 + )

→−4 4

4(−4)

16

Fo

√

2 √

2

√

√

√

√

√

√

1+ −

1−

1+− 1−

1+− 1−

1++ 1−

√

√

√

= lim

25. lim

= lim

·√

→0

→0

1 + + 1 − →0 1 + + 1 −

(1 + ) − (1 − )

2

2

= lim √

= lim √

√

√

√

= lim √

→0

→0

→0

1++ 1−

1++ 1−

1++ 1−

ot

2

2

√ = =1

= √

2

1+ 1

√

√

√

4−

(4 − )(4 + )

16 −

√

√

= lim

= lim

→16 16 − 2

→16 (16 − 2 )(4 +

) →16 (16 − )(4 + )

N

27. lim

= lim

→16

29. lim

→0

1

1

√

−

1+

1

1

1

1

√ =

√

=

=

16(8)

128

(4 + )

16 4 + 16

= lim

→0

√

√

√

1− 1+ 1+ 1+

1− 1+

−

= lim √

√

√

√

√

= lim

→0

→0

1+

+1 1+ 1+

1+ 1+ 1+

−1

−1

1

= √

=−

√

√

= lim √

→0

2

1+ 1+ 1+

1+0 1+ 1+0

31. lim

→0

( + )3 − 3

(3 + 32 + 32 + 3 ) − 3

32 + 32 + 3

= lim

= lim

→0

→0

= lim

→0

(32 + 3 + 2 )

= lim (32 + 3 + 2 ) = 32

→0

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

31

32

¤

CHAPTER 1

FUNCTIONS AND LIMITS

(b)

33. (a)

−0001

−00001

−000001

−0000001

0000001

000001

00001

0001

2

≈ lim √

3

1 + 3 − 1

→0

(c) lim

→0

()

06661663

06666167

06666617

06666662

06666672

06666717

06667167

06671663

The limit appears to be

2

.

3

√

√

√

1 + 3 + 1

1 + 3 + 1

1 + 3 + 1

√

= lim

·√

= lim

→0

→0

(1 + 3) − 1

3

1 + 3 − 1

1 + 3 + 1

√

1

1 + 3 + 1 lim 3 →0

1 lim (1 + 3) + lim 1

=

→0

→0

3

1

=

lim 1 + 3 lim + 1

→0

→0

3

[Limit Law 3]

e

=

al

[1 and 11]

1 √

1+3·0+1

3

[7 and 8]

1

2

(1 + 1) =

3

3

Fo

=

rS

=

[1, 3, and 7]

35. Let () = −2 , () = 2 cos 20 and () = 2 . Then

−1 ≤ cos 20 ≤ 1 ⇒ −2 ≤ 2 cos 20 ≤ 2

⇒ () ≤ () ≤ ().

So since lim () = lim () = 0, by the Squeeze Theorem we have

→0

→0

ot

lim () = 0.

→0

37. We have lim (4 − 9) = 4(4) − 9 = 7 and lim 2 − 4 + 7 = 42 − 4(4) + 7 = 7. Since 4 − 9 ≤ () ≤ 2 − 4 + 7

→4

N

→4

for ≥ 0, lim () = 7 by the Squeeze Theorem.

→4

39. −1 ≤ cos(2) ≤ 1

⇒ −4 ≤ 4 cos(2) ≤ 4 . Since lim −4 = 0 and lim 4 = 0, we have

→0

→0

lim 4 cos(2) = 0 by the Squeeze Theorem.

→0

41. | − 3| =

if − 3 ≥ 0

−3

if − 3 0

−( − 3)

=

−3

3−

if ≥ 3

if 3

Thus, lim (2 + | − 3|) = lim (2 + − 3) = lim (3 − 3) = 3(3) − 3 = 6 and

→3+

→3+

→3+

lim (2 + | − 3|) = lim (2 + 3 − ) = lim ( + 3) = 3 + 3 = 6. Since the left and right limits are equal,

→3−

→3−

→3−

lim (2 + | − 3|) = 6.

→3

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

SECTION 1.6

43. 23 − 2 = 2 (2 − 1) = 2 · |2 − 1| = 2 |2 − 1|

|2 − 1| =

2 − 1

−(2 − 1)

if 2 − 1 ≥ 0

if 2 − 1 0

=

2 − 1

CALCULATING LIMITS USING THE LIMIT LAWS

¤

if ≥ 05

if 05

−(2 − 1)

So 23 − 2 = 2 [−(2 − 1)] for 05.

Thus,

lim

→05−

2 − 1

2 − 1

−1

−1

−1

= lim

= lim

= −4.

=

=

|23 − 2 | →05− 2 [−(2 − 1)] →05− 2

(05)2

025

45. Since || = − for 0, we have lim

→0−

1

1

−

||

= lim

→0−

1

1

−

−

= lim

→0−

2

, which does not exist since the

denominator approaches 0 and the numerator does not.

47. (a)

(b) (i) Since sgn = 1 for 0, lim sgn = lim 1 = 1.

e

→0+

→0+

(ii) Since sgn = −1 for 0, lim sgn = lim −1 = −1.

al

→0−

→0−

(iii) Since lim sgn 6= lim sgn , lim sgn does not exist.

→0−

→0

→0+

(iv) Since |sgn | = 1 for 6= 0, lim |sgn | = lim 1 = 1.

49. (a) (i) lim () = lim

→2+

→2+

→0

rS

→0

2 + − 6

( + 3)( − 2)

= lim

| − 2|

| − 2|

→2+

= lim

( + 3)( − 2)

−2

Fo

→2+

[since − 2 0 if → 2+ ]

= lim ( + 3) = 5

→2+

(ii) The solution is similar to the solution in part (i), but now | − 2| = 2 − since − 2 0 if → 2− .

Thus, lim () = lim −( + 3) = −5.

→2−

ot

→2−

(b) Since the right-hand and left-hand limits of at = 2

(c)

N

are not equal, lim () does not exist.

→2

51. (a) (i) [[]] = −2 for −2 ≤ −1, so

→−2+

(ii) [[]] = −3 for −3 ≤ −2, so

→−2−

lim [[]] = lim [[]] =

lim (−2) = −2

→−2+

lim (−3) = −3.

→−2−

The right and left limits are different, so lim [[]] does not exist.

→−2

(iii) [[]] = −3 for −3 ≤ −2, so

lim [[]] =

→−24

lim (−3) = −3.

→−24

(b) (i) [[]] = − 1 for − 1 ≤ , so lim [[]] = lim ( − 1) = − 1.

→−

→−

(ii) [[]] = for ≤ + 1, so lim [[]] = lim = .

→+

→+

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

33

34

¤

CHAPTER 1

FUNCTIONS AND LIMITS

(c) lim [[]] exists ⇔ is not an integer.

→

53. The graph of () = [[]] + [[−]] is the same as the graph of () = −1 with holes at each integer, since () = 0 for any

integer . Thus, lim () = −1 and lim () = −1, so lim () = −1. However,

→2−

→2

→2+

(2) = [[2]] + [[−2]] = 2 + (−2) = 0, so lim () 6= (2).

→2

55. Since () is a polynomial, () = 0 + 1 + 2 2 + · · · + . Thus, by the Limit Laws,

lim () = lim 0 + 1 + 2 2 + · · · + = 0 + 1 lim + 2 lim 2 + · · · + lim

→

→

→

→

→

= 0 + 1 + 2 2 + · · · + = ()

Thus, for any polynomial , lim () = ().

→

→1

→1

() − 8

() − 8

· ( − 1) = lim

· lim ( − 1) = 10 · 0 = 0.

→1

→1

−1

−1

e

57. lim [() − 8] = lim

Thus, lim () = lim {[ () − 8] + 8} = lim [ () − 8] + lim 8 = 0 + 8 = 8.

→1

Note: The value of lim

→1

→1

() − 8 does not affect the answer since it’s multiplied by 0. What’s important is that

−1

() − 8 exists. −1

rS

lim

→1

→1

al

→1

59. Observe that 0 ≤ () ≤ 2 for all , and lim 0 = 0 = lim 2 . So, by the Squeeze Theorem, lim () = 0.

→0

→0

→0

Fo

61. Let () = () and () = 1 − (), where is the Heaviside function deﬁned in Exercise 1.3.57.

Thus, either or is 0 for any value of . Then lim () and lim () do not exist, but lim [ ()()] = lim 0 = 0.

→0

→0

→0

→0

63. Since the denominator approaches 0 as → −2, the limit will exist only if the numerator also approaches

ot

0 as → −2. In order for this to happen, we need lim

→−2

2

3 + + + 3 = 0 ⇔

lim

→−2

N

3(−2)2 + (−2) + + 3 = 0 ⇔ 12 − 2 + + 3 = 0 ⇔ = 15. With = 15, the limit becomes

32 + 15 + 18

3( + 2)( + 3)

3( + 3)

3(−2 + 3)

3

= lim

= lim

=

=

= −1.

→−2 ( − 1)( + 2)

→−2 − 1

2 + − 2

−2 − 1

−3

1.7 The Precise Definition of a Limit

1. If |() − 1| 02, then −02 () − 1 02

⇒ 08 () 12. From the graph, we see that the last inequality is

true if 07 11, so we can choose = min {1 − 07 11 − 1} = min {03 01} = 01 (or any smaller positive

number).

3. The leftmost question mark is the solution of

√

√

= 16 and the rightmost, = 24. So the values are 162 = 256 and

242 = 576. On the left side, we need | − 4| |256 − 4| = 144. On the right side, we need | − 4| |576 − 4| = 176.

To satisfy both conditions, we need the more restrictive condition to hold — namely, | − 4| 144. Thus, we can choose

= 144, or any smaller positive number.

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

SECTION 1.7

THE PRECISE DEFINITION OF A LIMIT

¤

35

From the graph, we ﬁnd that = tan = 08 when ≈ 0675, so

5.

4

− 1 ≈ 0675 ⇒ 1 ≈

when ≈ 0876, so

4

4

− 0675 ≈ 01106. Also, = tan = 12

+ 2 ≈ 0876 ⇒ 2 = 0876 −

4

≈ 00906.

Thus, we choose = 00906 (or any smaller positive number) since this is the smaller of 1 and 2 .

From the graph with = 02, we ﬁnd that = 3 − 3 + 4 = 58 when

7.

≈ 19774, so 2 − 1 ≈ 19774 ⇒ 1 ≈ 00226. Also,

= 3 − 3 + 4 = 62 when ≈ 2022, so 2 + 2 ≈ 20219 ⇒

2 ≈ 00219. Thus, we choose = 00219 (or any smaller positive number) since this is the smaller of 1 and 2 .

e

For = 01, we get 1 ≈ 00112 and 2 ≈ 00110, so we choose

al

= 0011 (or any smaller positive number).

9. (a)

From the graph, we ﬁnd that = tan2 = 1000 when ≈ 1539 and

.

2

Thus, we get ≈ 1602 −

rS

≈ 1602 for near

2

≈ 0031 for

= 1000.

From the graph, we ﬁnd that = tan2 = 10,000 when ≈ 1561 and

Fo

(b)

≈ 1581 for near

2.

Thus, we get ≈ 1581 −

2

≈ 0010 for

ot

= 10,000.

N

11. (a) = 2 and = 1000 cm2

⇒ 2 = 1000 ⇒ 2 =

1000

⇒ =

1000

( 0)

≈ 178412 cm.

(b) | − 1000| ≤ 5 ⇒ −5 ≤ 2 − 1000 ≤ 5 ⇒ 1000 − 5 ≤ 2 ≤ 1000 + 5 ⇒

995

1000

≤ ≤ 1005 ⇒ 177966 ≤ ≤ 178858.

− 995 ≈ 004466 and 1005 − 1000 ≈ 004455. So

if the machinist gets the radius within 00445 cm of 178412, the area will be within 5 cm2 of 1000.

(c) is the radius, () is the area, is the target radius given in part (a), is the target area (1000), is the tolerance in the area (5), and is the tolerance in the radius given in part (b).

13. (a) |4 − 8| = 4 | − 2| 01

⇔ | − 2|

01

01

, so =

= 0025.

4

4

(b) |4 − 8| = 4 | − 2| 001 ⇔ | − 2|

001

001

, so =

= 00025.

4

4

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

36

¤

CHAPTER 1

FUNCTIONS AND LIMITS

15. Given 0, we need 0 such that if 0 | − 3| , then

(1 + 1 ) − 2 . But (1 + 1 ) − 2 ⇔ 1 − 1 ⇔

3

3

3

1

| − 3| ⇔ | − 3| 3. So if we choose = 3, then

3

0 | − 3| ⇒ (1 + 1 ) − 2 . Thus, lim (1 + 1 ) = 2 by

3

3

→3

the deﬁnition of a limit.

17. Given 0, we need 0 such that if 0 | − (−3)| , then

|(1 − 4) − 13| . But |(1 − 4) − 13| ⇔

|−4 − 12| ⇔ |−4| | + 3| ⇔ | − (−3)| 4. So if we choose = 4, then 0 | − (−3)|

⇒ |(1 − 4) − 13| .

Thus, lim (1 − 4) = 13 by the deﬁnition of a limit.

e

→−3

al

2 + 4

19. Given 0, we need 0 such that if 0 | − 1| , then

x

2 + 4

− 2 . But

− 2 ⇔

3

Fo

rS

3

4 − 4

4

3

3

3 ⇔ 3 | − 1| ⇔ | − 1| 4 . So if we choose = 4 , then 0 | − 1|

2 + 4

2 + 4

− 2 . Thus, lim

= 2 by the deﬁnition of a limit.

3

→1

3

2

+ − 6

21. Given 0, we need 0 such that if 0 | − 2| , then

( + 3)( − 2)

− 5

−2

− 5 ⇔

| + 3 − 5| [ 6= 2] ⇔ | − 2| . So choose = .

( + 3)( − 2)

⇒ | − 2| ⇒ | + 3 − 5| ⇒

− 5 [ 6= 2] ⇒

−2

ot

Then 0 | − 2|

⇔

−2

⇒

N

2

+ − 6

2 + − 6

− 5 . By the deﬁnition of a limit, lim

= 5.

−2

→2

−2

23. Given 0, we need 0 such that if 0 | − | , then | − | . So = will work.

25. Given 0, we need 0 such that if 0 | − 0| , then 2 − 0

Then 0 | − 0|

⇔ 2

⇒ 2 − 0 . Thus, lim 2 = 0 by the deﬁnition of a limit.

⇔ ||

√

√

. Take = .

→0

27. Given 0, we need 0 such that if 0 | − 0| , then || − 0 . But || = ||. So this is true if we pick = .

Thus, lim || = 0 by the deﬁnition of a limit.

→0

⇔ 2 − 4 + 4 ⇔

√

⇔ | − 2| ⇔ ( − 2)2 . Thus,

29. Given 0, we need 0 such that if 0 | − 2| , then 2 − 4 + 5 − 1

( − 2)2 . So take = √. Then 0 | − 2|

lim 2 − 4 + 5 = 1 by the deﬁnition of a limit.

→2

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

SECTION 1.7

THE PRECISE DEFINITION OF A LIMIT

¤

37

31. Given 0, we need 0 such that if 0 | − (−2)| , then 2 − 1 − 3 or upon simplifying we need

2

− 4 whenever 0 | + 2| . Notice that if | + 2| 1, then −1 + 2 1 ⇒ −5 − 2 −3 ⇒

| − 2| 5. So take = min {5 1}. Then 0 | + 2| ⇒ | − 2| 5 and | + 2| 5, so

2

− 1 − 3 = |( + 2)( − 2)| = | + 2| | − 2| (5)(5) = . Thus, by the deﬁnition of a limit, lim (2 − 1) = 3.

→−2

. If 0 | − 3| , then | − 3| 2 ⇒ −2 − 3 2 ⇒

4 + 3 8 ⇒ | + 3| 8. Also | − 3| 8 , so 2 − 9 = | + 3| | − 3| 8 · 8 = . Thus, lim 2 = 9.

33. Given 0, we let = min 2

8

→3

35. (a) The points of intersection in the graph are (1 26) and (2 34)

with 1 ≈ 0891 and 2 ≈ 1093. Thus, we can take to be the

e

smaller of 1 − 1 and 2 − 1. So = 2 − 1 ≈ 0093.

rS

al

(b) Solving 3 + + 1 = 3 + gives us two nonreal complex roots and

√

23

− 12

216 + 108 + 12 336 + 324 + 812 one real root, which is () =

√

13 . Thus, = () − 1.

2

6 216 + 108 + 12 336 + 324 + 81

(c) If = 04, then () ≈ 1093 272 342 and = () − 1 ≈ 0093, which agrees with our answer in part (a).

37. 1. Guessing a value for

√

√

Given 0, we must ﬁnd 0 such that | − | whenever 0 | − | . But

Fo

√

√

√

√

| − |

√ (from the hint). Now if we can ﬁnd a positive constant such that + then

| − | = √

+

√

√

1

is a suitable choice for the constant. So | − |

+ . This suggests that we let

2

1

2

+

1

2

√

.

N

=

ot

| − |

| − |

√

√

, and we take | − | . We can ﬁnd this number by restricting to lie in some interval

+

√

√

√ centered at . If | − | 1 , then − 1 − 1 ⇒ 1 3 ⇒

+ 1 + , and so

2

2

2

2

2

2

= min

1

2

+

2. Showing that works

| − | 1 ⇒

2

Given 0, we let = min

1

2

1

2

+

√

. If 0 | − | , then

√

√

√

√

1

+ 1 + (as in part 1). Also | − |

+ , so

2

2

√

2 +

√

√

√

√

| − |

√

| − | = √ lim √ = . Therefore, → = by the deﬁnition of a limit.

+

2 +

39. Suppose that lim () = . Given =

→0

1

,

2

there exists 0 such that 0 ||

⇒ |() − | 1 . Take any rational

2

number with 0 || . Then () = 0, so |0 − | 1 , so ≤ || 1 . Now take any irrational number with

2

2

0 || . Then () = 1, so |1 − | 1 . Hence, 1 − 1 , so 1 . This contradicts 1 , so lim () does not

2

2

2

2

→0

exist. c ° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

38

¤

41.

1

1

10,000 ⇔ ( + 3)4

( + 3)4

10,000

CHAPTER 1

FUNCTIONS AND LIMITS

1

⇔ | + 3| √

4

10,000

⇔

| − (−3)|

1

10

5

5

5

3

43. Let 0 be given. Then, for −1, we have

⇔

( + 1) ⇔ 3

+ 1.

( + 1)3

5

5

5

5

. Then −1 − −1 ⇒ 3

+10 ⇒

, so lim

= −∞.

Let = − 3

( + 1)3

→−1− ( + 1)3

1.8 Continuity

1. From Deﬁnition 1, lim () = (4).

→4

3. (a) is discontinuous at −4 since (−4) is not deﬁned and at −2, 2, and 4 since the limit does not exist (the left and right

lim () = (−2). is continuous from the right at 2 and 4 since

→−2−

al

(b) is continuous from the left at −2 since

e

limits are not the same).

lim () = (2) and lim () = (4). It is continuous from neither side at −4 since (−4) is undeﬁned.

→4+

5. The graph of = () must have a discontinuity at

= 2 and must show that lim () = (2).

→2+

7. The graph of = () must have a removable

rS

→2+

discontinuity (a hole) at = 3 and a jump discontinuity

ot

Fo

at = 5.

N

9. (a) The toll is $7 between 7:00 AM and 10:00 AM and between 4:00 PM and 7:00 PM .

(b) The function has jump discontinuities at = 7, 10, 16, and 19. Their signiﬁcance to someone who uses the road is that, because of the sudden jumps in the toll, they may want to avoid the higher rates between = 7 and = 10 and between = 16 and = 19 if feasible.

11. If and are continuous and (2) = 6, then lim [3 () + () ()] = 36

→2

⇒

3 lim () + lim () · lim () = 36 ⇒ 3 (2) + (2) · 6 = 36 ⇒ 9 (2) = 36 ⇒ (2) = 4.

→2

→2

13. lim () = lim

→−1

→−1

→2

4

+ 23 =

lim + 2 lim 3

→−1

→−1

By the deﬁnition of continuity, is continuous at = −1.

4

4

= −1 + 2(−1)3 = (−3)4 = 81 = (−1).

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

SECTION 1.8

CONTINUITY

¤

15. For 2, we have

lim (2 + 3)

2 + 3

→

=

→ − 2 lim ( − 2)

lim () = lim

→

[Limit Law 5]

→

2 lim + lim 3

=

→

→

=

→

[1, 2, and 3]

lim − lim 2

→

2 + 3

−2

[7 and 8]

= ()

Thus, is continuous at = for every in (2 ∞); that is, is continuous on (2 ∞).

1

is discontinuous at = −2 because (−2) is undeﬁned.

+2

19. () =

1

if 1

rS

1 − 2

al

e

17. () =

if ≥ 1

The left-hand limit of at = 1 is

→1−

Fo

lim () = lim (1 − 2 ) = 0 The right-hand limit of at = 1 is

→1−

lim () = lim (1) = 1 Since these limits are not equal, lim ()

→1+

→1+

→1

does not exist and is discontinuous at 1. if 0

ot

cos

21. () = 0

1 − 2

if = 0

N

if 0

lim () = 1, but (0) = 0 6= 1, so is discontinuous at 0.

→0

23. () =

( − 2)( + 1)

2 − − 2

=

= + 1 for 6= 2. Since lim () = 2 + 1 = 3, deﬁne (2) = 3. Then is

→2

−2

−2

continuous at 2.

25. () =

22 − − 1 is a rational function, so it is continuous on its domain, (−∞ ∞), by Theorem 5(b).

2 + 1

27. 3 − 2 = 0

⇒ 3 = 2 ⇒ =

√

3

2, so () =

continuous everywhere by Theorem 5(a) and

√

3

√ √

−2

has domain −∞ 3 2 ∪ 3 2 ∞ . Now 3 − 2 is

3 −2

√

3

− 2 is continuous everywhere by Theorems 5(a), 7, and 9. Thus, is

continuous on its domain by part 5 of Theorem 4.

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

39

40

¤

CHAPTER 1

FUNCTIONS AND LIMITS

29. By Theorem 5, the polynomial 1 − 2 is continuous on (−∞ ∞). By Theorem 7, cos is continuous on its domain, R. By

Theorem 9, cos 1 − 2 is continuous on its domain, which is R.

31. () =

+1

+1

1 is deﬁned when

≥ 0 ⇒ + 1 ≥ 0 and 0 or + 1 ≤ 0 and 0 ⇒ 0

1+ =

or ≤ −1, so has domain (−∞ −1] ∪ (0 ∞). is the composite of a root function and a rational function, so it is continuous at every number in its domain by Theorems 7 and 9.

33.

=

1 is undeﬁned and hence discontinuous when

1 + sin

1 + sin = 0 ⇔ sin = −1 ⇔ = − + 2, an

2

integer. The ﬁgure shows discontinuities for = −1, 0, and 1; that

√

√

is continuous on [0 ∞), + 5 is continuous on [−5 ∞), so the

al

35. Because we are dealing with root functions, 5 +

5

3

≈ −785, − ≈ −157, and

≈ 471.

2

2

2

e

is, −

rS

√

5+ is continuous on [0 ∞). Since is continuous at = 4, lim () = (4) = 7 . quotient () = √

3

→4

5+

37. Because and cos are continuous on R, so is () = cos2 . Since is continuous at =

→4

39. () =

2

√

4

=

4

√ 2

1

2

= · = .

2

4 2

8

Fo

lim () =

,

4

if 1 if ≥ 1

lim () = lim

→1+

→1−

→1−

√

√

= 1. Thus, lim () exists and equals 1. Also, (1) = 1 = 1. Thus, is continuous at = 1.

→1

N

→1+

ot

By Theorem 5, since () equals the polynomial 2 on (−∞ 1), is continuous on (−∞ 1). By Theorem 7, since ()

√

equals the root function on (1 ∞) is continuous on (1 ∞). At = 1, lim () = lim 2 = 1 and

We conclude that is continuous on (−∞ ∞).

1 + 2

41. () = 2 −

( − 2)2

if ≤ 0

if 0 ≤ 2 if 2

is continuous on (−∞ 0), (0 2), and (2 ∞) since it is a polynomial on each of these intervals. Now lim () = lim (1 + 2 ) = 1 and lim () = lim (2 − ) = 2 so is

→0−

→0−

→0+

→0+

discontinuous at 0. Since (0) = 1, is continuous from the left at 0 Also, lim () = lim (2 − ) = 0

→2−

→2−

lim () = lim ( − 2)2 = 0, and (2) = 0, so is continuous at 2 The only number at which is discontinuous is 0.

→2+

→2+

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

SECTION 1.8

+ 2

43. () = 22

2−

CONTINUITY

¤

41

if 0 if 0 ≤ ≤ 1 if 1

is continuous on (−∞ 0), (0 1), and (1 ∞) since on each of

these intervals it is a polynomial. Now lim () = lim ( + 2) = 2 and

→0−

→0−

lim () = lim 2 = 0, so is discontinuous at 0. Since (0) = 0, is continuous from the right at 0. Also

2

→0+

→0+

lim () = lim 22 = 2 and lim () = lim (2 − ) = 1, so is discontinuous at 1. Since (1) = 2,

→1−

→1−

→1+

→1+

is continuous from the left at 1.

2 + 2

3

−

if 2 if ≥ 2

is continuous on (−∞ 2) and (2 ∞). Now lim () = lim

→2−

3

− = 8 − 2. So is continuous ⇔ 4 + 4 = 8 − 2 ⇔ 6 = 4 ⇔ = 2 . Thus, for

3

to be continuous on (−∞ ∞), = 2 .

3

47. (a) () =

al

→2+

2

+ 2 = 4 + 4 and

rS

lim () = lim

→2+

→2−

e

45. () =

4 − 1

(2 + 1)(2 − 1)

(2 + 1)( + 1)( − 1)

=

=

= (2 + 1)( + 1) [or 3 + 2 + + 1]

−1

−1

−1

(b) () =

Fo

for 6= 1. The discontinuity is removable and () = 3 + 2 + + 1 agrees with for 6= 1 and is continuous on R.

(2 − − 2)

( − 2)( + 1)

3 − 2 − 2

=

=

= ( + 1) [or 2 + ] for 6= 2. The discontinuity

−2

−2

−2

ot

is removable and () = 2 + agrees with for 6= 2 and is continuous on R.

(c) lim () = lim [[sin ]] = lim 0 = 0 and lim () = lim [[sin ]] = lim (−1) = −1, so lim () does not

→−

→ −

→ −

→ +

→ +

→ +

→

N

exist. The discontinuity at = is a jump discontinuity.

49. () = 2 + 10 sin is continuous on the interval [31 32], (31) ≈ 957, and (32) ≈ 1030. Since 957 1000 1030,

there is a number c in (31 32) such that () = 1000 by the Intermediate Value Theorem. Note: There is also a number c in

(−32 −31) such that () = 1000

51. () = 4 + − 3 is continuous on the interval [1 2] (1) = −1, and (2) = 15. Since −1 0 15, there is a number

in (1 2) such that () = 0 by the Intermediate Value Theorem. Thus, there is a root of the equation 4 + − 3 = 0 in the interval (1 2)

53. () = cos − is continuous on the interval [0 1], (0) = 1, and (1) = cos 1 − 1 ≈ −046. Since −046 0 1, there

is a number in (0 1) such that () = 0 by the Intermediate Value Theorem. Thus, there is a root of the equation cos − = 0, or cos = , in the interval (0 1). c ° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

42

¤

CHAPTER 1

FUNCTIONS AND LIMITS

55. (a) () = cos − 3 is continuous on the interval [0 1], (0) = 1 0, and (1) = cos 1 − 1 ≈ −046 0. Since

1 0 −046, there is a number in (0 1) such that () = 0 by the Intermediate Value Theorem. Thus, there is a root of the equation cos − 3 = 0, or cos = 3 , in the interval (0 1).

(b) (086) ≈ 0016 0 and (087) ≈ −0014 0, so there is a root between 086 and 087, that is, in the interval

(086 087).

57. (a) Let () = 5 − 2 − 4. Then (1) = 15 − 12 − 4 = −4 0 and (2) = 25 − 22 − 4 = 24 0. So by the

Intermediate Value Theorem, there is a number in (1 2) such that () = 5 − 2 − 4 = 0.

al

e

(b) We can see from the graphs that, correct to three decimal places, the root is ≈ 1434.

lim ( + ) = lim ( + ) = ().

→0

→0

rS

59. (⇒) If is continuous at , then by Theorem 8 with () = + , we have

(⇐) Let 0. Since lim ( + ) = (), there exists 0 such that 0 ||

⇒

Fo

→0

| ( + ) − ()| . So if 0 | − | , then | () − ()| = | ( + ( − )) − ()| .

Thus, lim () = () and so is continuous at .

→

61. As in the previous exercise, we must show that lim cos( + ) = cos to prove that the cosine function is continuous.

ot

→0

lim cos( + ) = lim (cos cos − sin sin ) = lim (cos cos ) − lim (sin sin )

→0

→0

63. () =

→0

0 if is rational

1 if is irrational

→0

→0

lim cos lim cos − lim sin lim sin = (cos )(1) − (sin )(0) = cos

N

=

→0

→0

→0

is continuous nowhere. For, given any number and any 0, the interval ( − + )

contains both inﬁnitely many rational and inﬁnitely many irrational numbers. Since () = 0 or 1, there are inﬁnitely many numbers with 0 | − | and | () − ()| = 1. Thus, lim () 6= (). [In fact, lim () does not even exist.]

→

65. If there is such a number, it satisﬁes the equation 3 + 1 =

→

⇔ 3 − + 1 = 0. Let the left-hand side of this equation be

called (). Now (−2) = −5 0, and (−1) = 1 0. Note also that () is a polynomial, and thus continuous. So by the

Intermediate Value Theorem, there is a number between −2 and −1 such that () = 0, so that = 3 + 1.

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

CHAPTER 1 REVIEW

¤

43

67. () = 4 sin(1) is continuous on (−∞ 0) ∪ (0 ∞) since it is the product of a polynomial and a composite of a

trigonometric function and a rational function. Now since −1 ≤ sin(1) ≤ 1, we have −4 ≤ 4 sin(1) ≤ 4 . Because lim (−4 ) = 0 and lim 4 = 0, the Squeeze Theorem gives us lim (4 sin(1)) = 0, which equals (0). Thus, is

→0

→0

→0

continuous at 0 and, hence, on (−∞ ∞).

69. Deﬁne () to be the monk’s distance from the monastery, as a function of time (in hours), on the ﬁrst day, and deﬁne ()

to be his distance from the monastery, as a function of time, on the second day. Let be the distance from the monastery to the top of the mountain. From the given information we know that (0) = 0, (12) = , (0) = and (12) = 0. Now consider the function − , which is clearly continuous. We calculate that ( − )(0) = − and ( − )(12) = .

So by the Intermediate Value Theorem, there must be some time 0 between 0 and 12 such that ( − )(0 ) = 0 ⇔

e

(0 ) = (0 ). So at time 0 after 7:00 AM, the monk will be at the same place on both days.

rS

al

1 REVIEW

1. (a) A function is a rule that assigns to each element in a set exactly one element, called (), in a set . The set is

called the domain of the function. The range of is the set of all possible values of () as varies throughout the domain. Fo

(b) If is a function with domain , then its graph is the set of ordered pairs {( ()) | ∈ }.

(c) Use the Vertical Line Test on page 15.

2. The four ways to represent a function are: verbally, numerically, visually, and algebraically. An example of each is given

ot

below.

Verbally: An assignment of students to chairs in a classroom (a description in words)

Numerically: A tax table that assigns an amount of tax to an income (a table of values)

N

Visually: A graphical history of the Dow Jones average (a graph)

Algebraically: A relationship between distance, rate, and time: = (an explicit formula)

3. (a) If a function satisﬁes (−) = () for every number in its domain, then is called an even function. If the graph of

a function is symmetric with respect to the -axis, then is even. Examples of an even function: () = 2 ,

() = 4 + 2 , () = ||, () = cos .

(b) If a function satisﬁes (−) = − () for every number in its domain, then is called an odd function. If the graph of a function is symmetric with respect to the origin, then is odd. Examples of an odd function: () = 3 ,

√

() = 3 + 5 , () = 3 , () = sin .

4. A function is called increasing on an interval if (1 ) (2 ) whenever 1 2 in .

5. A mathematical model is a mathematical description (often by means of a function or an equation) of a real-world

phenomenon. c ° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

44

¤

CHAPTER 1

FUNCTIONS AND LIMITS

6. (a) Linear function: () = 2 + 1, () = +

7.

(b) Power function: () = , () =

2

(c) Exponential function: () = 2 , () =

(d) Quadratic function: () = 2 + + 1, () = 2 + +

(e) Polynomial of degree 5: () = 5 + 2

(f ) Rational function: () =

()

, () = where () and

+2

()

() are polynomials

(b)

(d)

Fo

rS

(c)

al

e

8. (a)

(f )

N

ot

(e )

9. (a) The domain of + is the intersection of the domain of and the domain of ; that is, ∩ .

(b) The domain of is also ∩ .

(c) The domain of must exclude values of that make equal to 0; that is, { ∈ ∩ | () 6= 0}.

10. Given two functions and , the composite function ◦ is deﬁned by ( ◦ ) () = ( ()). The domain of ◦ is the

set of all in the domain of such that () is in the domain of .

11. (a) If the graph of is shifted 2 units upward, its equation becomes = () + 2.

(b) If the graph of is shifted 2 units downward, its equation becomes = () − 2.

(c) If the graph of is shifted 2 units to the right, its equation becomes = ( − 2).

(d) If the graph of is shifted 2 units to the left, its equation becomes = ( + 2).

(e) If the graph of is reﬂected about the -axis, its equation becomes = − ().

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

CHAPTER 1 REVIEW

¤

45

(f ) If the graph of is reﬂected about the -axis, its equation becomes = (−).

(g) If the graph of is stretched vertically by a factor of 2, its equation becomes = 2 ().

(h) If the graph of is shrunk vertically by a factor of 2, its equation becomes = 1 ().

2

(i) If the graph of is stretched horizontally by a factor of 2, its equation becomes = 1 .

2

(j) If the graph of is shrunk horizontally by a factor of 2, its equation becomes = (2).

12. (a) lim () = : See Deﬁnition 1.5.1 and Figures 1 and 2 in Section 1.5.

→

(b) lim () = : See the paragraph after Deﬁnition 1.5.2 and Figure 9(b) in Section 1.5.

→+

(c) lim () = : See Deﬁnition 1.5.2 and Figure 9(a) in Section 1.5.

→−

(d) lim () = ∞: See Deﬁnition 1.5.4 and Figure 12 in Section 1.5.

→

(e) lim () = −∞: See Deﬁnition 1.5.5 and Figure 13 in Section 1.5.

→

e

13. In general, the limit of a function fails to exist when the function does not approach a ﬁxed number. For each of the following

Fo

rS

al

functions, the limit fails to exist at = 2.

The left- and right-hand

There is an

There are an inﬁnite

limits are not equal.

inﬁnite discontinuity.

number of oscillations.

ot

14. See Deﬁnition 1.5.6 and Figures 12–14 in Section 1.5.

15. (a) – (g) See the statements of Limit Laws 1– 6 and 11 in Section 1.6.

N

16. See Theorem 3 in Section 1.6.

17. (a) A function is continuous at a number if () approaches () as approaches ; that is, lim () = ().

→

(b) A function is continuous on the interval (−∞ ∞) if is continuous at every real number . The graph of such a function has no breaks and every vertical line crosses it.

18. See Theorem 1.8.10.

1. False.

Let () = 2 , = −1, and = 1. Then ( + ) = (−1 + 1)2 = 02 = 0, but

() + () = (−1)2 + 12 = 2 6= 0 = ( + ).

3. False.

Let () = 2 . Then (3) = (3)2 = 92 and 3 () = 32 . So (3) 6= 3 (). c ° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

46

¤

CHAPTER 1

FUNCTIONS AND LIMITS

5. True.

See the Vertical Line Test.

7. False.

Limit Law 2 applies only if the individual limits exist (these don’t).

9. True.

Limit Law 5 applies.

11. False.

Consider lim

→5

( − 5) sin( − 5) or lim

. The ﬁrst limit exists and is equal to 5. By Example 3 in Section 1.5,

→5

−5

−5

we know that the latter limit exists (and it is equal to 1).

13. True.

Suppose that lim [ () + ()] exists. Now lim () exists and lim () does not exist, but

→

→

→

lim () = lim {[ () + ()] − ()} = lim [ () + ()] − lim () [by Limit Law 2], which exists, and

→

→

→

→

we have a contradiction. Thus, lim [ () + ()] does not exist.

→

A polynomial is continuous everywhere, so lim () exists and is equal to ().

→

1( − 1) if 6= 1

e

15. True.

Consider () =

19. True.

Use Theorem 1.8.8 with = 2, = 5, and () = 42 − 11. Note that (4) = 3 is not needed.

rS

if = 1

2

21. True, by the deﬁnition of a limit with = 1.

23. True.

al

17. False.

() = 10 − 102 + 5 is continuous on the interval [0 2], (0) = 5, (1) = −4, and (2) = 989. Since

Fo

−4 0 5, there is a number in (0 1) such that () = 0 by the Intermediate Value Theorem. Thus, there is a root of the equation 10 − 102 + 5 = 0 in the interval (0 1). Similarly, there is a root in (1 2).

See Exercise 68(c) in Section 1.8.

ot

25. False

N

1. (a) When = 2, ≈ 27. Thus, (2) ≈ 27.

(c) The domain of is −6 ≤ ≤ 6, or [−6 6].

(b) () = 3 ⇒ ≈ 23, 56

(d) The range of is −4 ≤ ≤ 4, or [−4 4].

(e) is increasing on [−4 4], that is, on −4 ≤ ≤ 4.

(f) is odd since its graph is symmetric about the origin.

3. () = 2 − 2 + 3, so ( + ) = ( + )2 − 2( + ) + 3 = 2 + 2 + 2 − 2 − 2 + 3, and

(2 + 2 + 2 − 2 − 2 + 3) − (2 − 2 + 3)

(2 + − 2)

( + ) − ()

=

=

= 2 + − 2.

5. () = 2(3 − 1).

Domain: 3 − 1 6= 0 ⇒ 3 6= 1 ⇒ 6= 1 . = −∞ 1 ∪ 1 ∞

3

3

3

Range:

7. = 1 + sin .

all reals except 0 ( = 0 is the horizontal asymptote for .) = (−∞ 0) ∪ (0 ∞)

Domain: R.

Range:

−1 ≤ sin ≤ 1 ⇒ 0 ≤ 1 + sin ≤ 2 ⇒ 0 ≤ ≤ 2. = [0 2]

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

CHAPTER 1 REVIEW

¤

47

9. (a) To obtain the graph of = () + 8, we shift the graph of = () up 8 units.

(b) To obtain the graph of = ( + 8), we shift the graph of = () left 8 units.

(c) To obtain the graph of = 1 + 2 (), we stretch the graph of = () vertically by a factor of 2, and then shift the resulting graph 1 unit upward.

(d) To obtain the graph of = ( − 2) − 2, we shift the graph of = () right 2 units (for the “−2” inside the parentheses), and then shift the resulting graph 2 units downward.

(e) To obtain the graph of = − (), we reﬂect the graph of = () about the -axis.

(f) To obtain the graph of = 3 − (), we reﬂect the graph of = () about the -axis, and then shift the resulting graph

3 units upward.

13. = 1 + 1 3 : Start with the

2

graph of = 3 , compress

shift 1 unit upward.

1

:

+2

ot

15. () =

Fo

vertically by a factor of 2, and

rS

al

e

11. = − sin 2: Start with the graph of = sin , compress horizontally by a factor of 2, and reﬂect about the -axis.

Start with the graph of () = 1

N

and shift 2 units to the left.

17. (a) The terms of are a mixture of odd and even powers of , so is neither even nor odd.

(b) The terms of are all odd powers of , so is odd.

(c) (−) = cos (−)2 = cos(2 ) = (), so is even.

(d) (−) = 1 + sin(−) = 1 − sin . Now (−) 6= () and (−) 6= −(), so is neither even nor odd.

19. () =

√

, = [0 ∞); () = sin , = R.

(a) ( ◦ )() = (()) = (sin ) =

√

√

sin . For sin to be deﬁned, we must have sin ≥ 0 ⇔

∈ [0 ], [2 3], [−2 −], [4 5], [−4 −3], , so = { | ∈ [2 + 2] , where is an integer}.

√

√

√

(b) ( ◦ )() = ( ()) = ( ) = sin . must be greater than or equal to 0 for to be deﬁned, so = [0 ∞). c ° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

48

¤

CHAPTER 1

FUNCTIONS AND LIMITS

√

√

√

4

(c) ( ◦ )() = ( ()) = ( ) =

= . = [0 ∞).

(d) ( ◦ )() = (()) = (sin ) = sin(sin ). = R.

Many models appear to be plausible. Your choice depends on whether you

21.

think medical advances will keep increasing life expectancy, or if there is bound to be a natural leveling-off of life expectancy. A linear model,

= 02493 − 4234818, gives us an estimate of 776 years for the

year 2010.

23. (a) (i) lim () = 3

(ii)

→2+

lim () = 0

→−3+

(iii) lim () does not exist since the left and right limits are not equal. (The left limit is −2.)

→−3

(iv) lim () = 2

e

→4

(v) lim () = ∞

(vi) lim () = −∞

→0

(b) The equations of the vertical asymptotes are = 0 and = 2.

al

→2−

25. lim cos( + sin ) = cos

→0

→−3

29. lim

→0

lim ( + sin ) [by Theorem 1.8.8] = cos 0 = 1

→0

2 − 9

( + 3)( − 3)

−3

−3 − 3

−6

3

= lim

= lim

=

=

=

2 + 2 − 3 →−3 ( + 3)( − 1) →−3 − 1

−3 − 1

−4

2

Fo

27. lim

rS

(c) is discontinuous at = −3, 0, 2, and 4. The discontinuities are jump, inﬁnite, inﬁnite, and removable, respectively.

3

− 32 + 3 − 1 + 1

( − 1)3 + 1

3 − 32 + 3

= lim

= lim

= lim 2 − 3 + 3 = 3

→0

→0

→0

N

ot

Another solution: Factor the numerator as a sum of two cubes and then simplify.

[( − 1) + 1] ( − 1)2 − 1( − 1) + 12

( − 1)3 + 1

( − 1)3 + 13

= lim

= lim lim →0

→0

→0

= lim ( − 1)2 − + 2 = 1 − 0 + 2 = 3

→0

√

√

4

+

31. lim

= ∞ since ( − 9) → 0 as → 9 and

0 for 6= 9.

→9 ( − 9)4

( − 9)4

33. lim

→1 3

4 − 1

(2 + 1)(2 − 1)

(2 + 1)( + 1)( − 1)

(2 + 1)( + 1)

2(2)

4

= lim

= lim

= lim

=

=

2 − 6

2 + 5 − 6)

→1 (

→1

→1

+ 5

( + 6)( − 1)

( + 6)

1(7)

7

√

√

4−

4−

−1

1

−1

√

= lim √

=−

= lim √

= √

→16 − 16

→16 ( + 4)( − 4)

→16

8

+4

16 + 4

35. lim

37. lim

→0

1−

√

√

1 − (1 − 2 )

1 − 2 1 + 1 − 2

2

√

√

√

√

= lim

= lim

= lim

=0

·

→0 1 +

→0 1 +

→0 1 +

1 + 1 − 2

1 − 2

1 − 2

1 − 2

39. Since 2 − 1 ≤ () ≤ 2 for 0 3 and lim (2 − 1) = 1 = lim 2 , we have lim () = 1 by the Squeeze Theorem.

→1

→1

→1

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

CHAPTER 1 REVIEW

41. Given 0, we need 0 such that if 0 | − 2| , then |(14 − 5) − 4| . But |(14 − 5) − 4|

|−5 + 10|

⇔

|−5| | − 2| ⇔ | − 2| 5. So if we choose = 5, then 0 | − 2|

¤

⇔

⇒

|(14 − 5) − 4| . Thus, lim (14 − 5) = 4 by the deﬁnition of a limit.

→2

43. Given 0, we need 0 so that if 0 | − 2| , then 2 − 3 − (−2) . First, note that if | − 2| 1, then

−1 − 2 1, so 0 − 1 2 ⇒ | − 1| 2. Now let = min {2 1}. Then 0 | − 2|

2

− 3 − (−2) = |( − 2)( − 1)| = | − 2| | − 1| (2)(2) = .

⇒

Thus, lim (2 − 3) = −2 by the deﬁnition of a limit.

→2

45. (a) () =

√

− if 0, () = 3 − if 0 ≤ 3, () = ( − 3)2 if 3.

(ii) lim () = lim

(i) lim () = lim (3 − ) = 3

→0+

→0−

→0+

(iv) lim () = lim (3 − ) = 0

→0

→3−

2

(v) lim () = lim ( − 3) = 0

→3−

(vi) Because of (iv) and (v), lim () = 0.

→3+

(b) is discontinuous at 0 since lim () does not exist.

→3

(c)

rS

→0

al

→3+

√

− = 0

e

(iii) Because of (i) and (ii), lim () does not exist.

→0−

is discontinuous at 3 since (3) does not exist.

The root function domain, [0 ∞).

Fo

47. 3 is continuous on R since it is a polynomial and cos is also continuous on R, so the product 3 cos is continuous on R.

√

√

4

4

is continuous on its domain, [0 ∞), and so the sum, () = + 3 cos , is continuous on its

ot

49. () = 5 − 3 + 3 − 5 is continuous on the interval [1 2], (1) = −2, and (2) = 25. Since −2 0 25, there is a

number in (1 2) such that () = 0 by the Intermediate Value Theorem. Thus, there is a root of the equation

N

5 − 3 + 3 − 5 = 0 in the interval (1 2).

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

49

N ot e

al

rS

Fo

PRINCIPLES OF PROBLEM SOLVING

1. Remember that || = if ≥ 0 and that || = − if 0. Thus,

+ || =

2 if ≥ 0

and

if 0

0

We will consider the equation + || = + || in four cases.

(1) ≥ 0 ≥ 0

2 = 2

(2) ≥ 0, 0

2 = 0

=

=0

(3) 0, ≥ 0

0 = 2

+ || =

2

0

if ≥ 0

if 0

(4) 0 0

0=0

0=

Case 1 gives us the line = with nonnegative and .

Case 2 gives us the portion of the -axis with negative.

e

Case 3 gives us the portion of the -axis with negative.

3. 0 () = 2 and +1 () = 0 ( ()) for = 0 1 2 .

al

Case 4 gives us the entire third quadrant.

rS

2

1 () = 0 (0 ()) = 0 2 = 2 = 4 , 2 () = 0 (1 ()) = 0 (4 ) = (4 )2 = 8 ,

+1

3 () = 0 (2 ()) = 0 (8 ) = (8 )2 = 16 , . Thus, a general formula is () = 2

5. Let =

.

√

6

, so = 6 . Then → 1 as → 1, so

Fo

√

3

−1

2 − 1

( − 1)( + 1)

+1

1+1

2

= lim 3 lim √

= lim

= lim 2

= 2

= .

→1

→1 − 1

→1 ( − 1) (2 + + 1)

→1 + + 1

1 +1+1

3

−1

√

√

√

3

2 + 3 + 1 .

Another method: Multiply both the numerator and the denominator by ( + 1)

Therefore, lim

we have 2 − 1 0 and 2 + 1 0, so |2 − 1| = −(2 − 1) and |2 + 1| = 2 + 1.

|2 − 1| − |2 + 1|

−(2 − 1) − (2 + 1)

−4

= lim

= lim

= lim (−4) = −4.

→0

→0

→0

N

→0

1

,

2

ot

7. For − 1

2

9. (a) For 0 1, [[]] = 0, so

lim

→0−

[[]]

= lim

→0−

−1

[[]]

[[]]

−1

[[]]

= 0, and lim

= 0. For −1 0, [[]] = −1, so

=

, and

→0+

= ∞. Since the one-sided limits are not equal, lim

→0

[[]] does not exist.

(b) For 0, 1 − 1 ≤ [[1]] ≤ 1 ⇒ (1 − 1) ≤ [[1]] ≤ (1) ⇒ 1 − ≤ [[1]] ≤ 1.

As → 0+ , 1 − → 1, so by the Squeeze Theorem, lim [[1]] = 1.

→0+

For 0, 1 − 1 ≤ [[1]] ≤ 1 ⇒ (1 − 1) ≥ [[1]] ≥ (1) ⇒ 1 − ≥ [[1]] ≥ 1.

As → 0− , 1 − → 1, so by the Squeeze Theorem, lim [[1]] = 1.

→0−

Since the one-sided limits are equal, lim [[1]] = 1.

→0

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

51

52

¤

CHAPTER 1 PRINCIPLES OF PROBLEM SOLVING

11. is continuous on (−∞ ) and ( ∞). To make continuous on R, we must have continuity at . Thus,

lim () = lim () ⇒

→−

→+

lim 2 = lim ( + 1) ⇒ 2 = + 1 ⇒ 2 − − 1 = 0 ⇒

→−

→+

√

[by the quadratic formula] = 1 ± 5 2 ≈ 1618 or −0618.

13. lim () = lim

→

→

=

1

2

1

2

·2+

and lim () = lim

→

[ () + ()] +

→

1

2

[() − ()] =

1

2

· 1 = 3,

2

+ ()] +

1 lim [ ()

2 →

[ () + ()] − () = lim [ () + ()] − lim () = 2 −

→

So lim [ ()()] = lim () lim () =

→

1 lim [ ()

2 →

→

→

3

2

·

1

2

→

3

2

− ()]

= 1.

2

= 3.

4

Another solution: Since lim [ () + ()] and lim [ () − ()] exist, we must have

→

→

→

lim [ () ()] = lim 1 [ () + ()]2 − [ () − ()]2

4

→

=

1

4

[because all of the 2 and 2 cancel]

lim [ () + ()]2 − lim [ () − ()]2 = 1 22 − 12 = 3 .

4

4

→

→

rS

→

→

e

lim [ () + ()]2 =

→

→

2

2 lim [ () + ()] and lim [ () − ()]2 = lim [ () − ()] , so

al

15. (a) Consider () = ( + 180◦ ) − (). Fix any number . If () = 0, we are done: Temperature at = Temperature

at + 180◦ . If () 0, then ( + 180◦ ) = ( + 360◦ ) − ( + 180◦ ) = () − ( + 180◦ ) = −() 0.

Fo

Also, is continuous since temperature varies continuously. So, by the Intermediate Value Theorem, has a zero on the interval [ + 180◦ ]. If () 0, then a similar argument applies.

(b) Yes. The same argument applies.

ot

(c) The same argument applies for quantities that vary continuously, such as barometric pressure. But one could argue that

N

altitude above sea level is sometimes discontinuous, so the result might not always hold for that quantity.

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

2

DERIVATIVES

2.1 Derivatives and Rates of Change

1. (a) This is just the slope of the line through two points: =

∆

() − (3)

=

.

∆

−3

(b) This is the limit of the slope of the secant line as approaches : = lim

→3

() − (3)

.

−3

3. (a) (i) Using Deﬁnition 1 with () = 4 − 2 and (1 3),

→

() − ()

(4 − 2 ) − 3

−(2 − 4 + 3)

−( − 1)( − 3)

= lim

= lim

= lim

→1

→1

→1

−

−1

−1

−1

e

= lim

= lim (3 − ) = 3 − 1 = 2

(ii) Using Equation 2 with () = 4 − 2 and (1 3),

al

→1

4(1 + ) − (1 + )2 − 3

( + ) − ()

(1 + ) − (1)

= lim

= lim

→0

→0

→0

rS

= lim

4 + 4 − 1 − 2 − 2 − 3

−2 + 2

(− + 2)

= lim

= lim

= lim (− + 2) = 2

→0

→0

→0

→0

= lim

or = 2 + 1.

(c)

Fo

(b) An equation of the tangent line is − () = 0 ()( − ) ⇒ − (1) = 0 (1)( − 1) ⇒ − 3 = 2( − 1),

The graph of = 2 + 1 is tangent to the graph of = 4 − 2 at the

point (1 3). Now zoom in toward the point (1 3) until the parabola and

N

ot

the tangent line are indistiguishable.

5. Using (1) with () = 4 − 32 and (2 −4) [we could also use (2)],

4 − 32 − (−4)

() − ()

−32 + 4 + 4

= lim

= lim

= lim

→

→2

→2

−

−2

−2

= lim

→2

(−3 − 2)( − 2)

= lim (−3 − 2) = −3(2) − 2 = −8

→2

−2

Tangent line: − (−4) = −8( − 2) ⇔ + 4 = −8 + 16 ⇔ = −8 + 12.

√

√

√

√

( − 1)( + 1)

− 1

−1

1

1

√

√

7. Using (1), = lim

= lim

= lim √

= .

= lim

→1

→1 ( − 1)( + 1)

→1 ( − 1)( + 1)

→1

−1

2

+1

Tangent line: − 1 = 1 ( − 1) ⇔

2

= 1 +

2

1

2

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

53

54

¤

CHAPTER 2

DERIVATIVES

9. (a) Using (2) with = () = 3 + 42 − 23 ,

( + ) − ()

3 + 4( + )2 − 2( + )3 − (3 + 42 − 23 )

= lim

→0

→0

= lim

3 + 4(2 + 2 + 2 ) − 2(3 + 32 + 32 + 3 ) − 3 − 42 + 23

→0

= lim

3 + 42 + 8 + 42 − 23 − 62 − 62 − 23 − 3 − 42 + 23

→0

= lim

8 + 42 − 62 − 62 − 23

(8 + 4 − 62 − 6 − 22 )

= lim

→0

→0

= lim

= lim (8 + 4 − 62 − 6 − 22 ) = 8 − 62

→0

(b) At (1 5): = 8(1) − 6(1)2 = 2, so an equation of the tangent line

(c)

is − 5 = 2( − 1) ⇔ = 2 + 3.

al

line is − 3 = −8( − 2) ⇔ = −8 + 19.

e

At (2 3): = 8(2) − 6(2)2 = −8, so an equation of the tangent

rS

11. (a) The particle is moving to the right when is increasing; that is, on the intervals (0 1) and (4 6). The particle is moving to

the left when is decreasing; that is, on the interval (2 3). The particle is standing still when is constant; that is, on the intervals (1 2) and (3 4).

Fo

(b) The velocity of the particle is equal to the slope of the tangent line of the

graph. Note that there is no slope at the corner points on the graph. On the interval (0 1) the slope is

3−0

= 3. On the interval (2 3), the slope is

1−0

13. Let () = 40 − 162 .

ot

1−3

3−1

= −2. On the interval (4 6), the slope is

= 1.

3−2

6−4

N

40 − 162 − 16

−8 22 − 5 + 2

() − (2)

−162 + 40 − 16

= lim

= lim

= lim

→2

→2

→2

→2

−2

−2

−2

−2

(2) = lim

= lim

→2

−8( − 2)(2 − 1)

= −8 lim (2 − 1) = −8(3) = −24

→2

−2

Thus, the instantaneous velocity when = 2 is −24 fts.

1

1

2 − ( + )2

− 2

( + ) − ()

( + )2

2 ( + )2

2 − (2 + 2 + 2 )

= lim

= lim

= lim

15. () = lim

→0

→0

→0

→0

2 ( + )2

−(2 + 2 )

−(2 + )

−(2 + )

−2

−2

= lim

= lim 2

= 2 2 = 3 ms

→0 2 ( + )2

→0 2 ( + )2

→0 ( + )2

·

= lim

So (1) =

−2

−2

−2

1

2 ms. = −2 ms, (2) = 3 = − ms, and (3) = 3 = −

13

2

4

3

27

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

SECTION 2.1

DERIVATIVES AND RATES OF CHANGE

¤

17. 0 (0) is the only negative value. The slope at = 4 is smaller than the slope at = 2 and both are smaller than the slope

at = −2. Thus, 0 (0) 0 0 (4) 0 (2) 0 (−2).

19. For the tangent line = 4 − 5: when = 2, = 4(2) − 5 = 3 and its slope is 4 (the coefﬁcient of ). At the point of

tangency, these values are shared with the curve = (); that is, (2) = 3 and 0 (2) = 4.

21. We begin by drawing a curve through the origin with a

slope of 3 to satisfy (0) = 0 and 0 (0) = 3. Since

0 (1) = 0, we will round off our ﬁgure so that there is a horizontal tangent directly over = 1. Last, we make sure that the curve has a slope of −1 as we pass over = 2. Two of the many possibilities are shown.

= lim

→0

(1 + ) − (1)

[3(1 + )2 − (1 + )3 ] − 2

= lim

→0

al

→0

(3 + 6 + 32 ) − (1 + 3 + 32 + 3 ) − 2

3 − 3

(3 − 2 )

= lim

= lim

→0

→0

rS

0 (1) = lim

e

23. Using (4) with () = 32 − 3 and = 1,

= lim (3 − 2 ) = 3 − 0 = 3

→0

Tangent line: − 2 = 3( − 1) ⇔ − 2 = 3 − 3 ⇔ = 3 − 1

Fo

25. (a) Using (4) with () = 5(1 + 2 ) and the point (2 2), we have

(b)

5(2 + )

−2

(2 + ) − (2)

1 + (2 + )2

(2) = lim

= lim

→0

→0

0

ot

5 + 10

5 + 10 − 2(2 + 4 + 5)

−2

+ 4 + 5

2 + 4 + 5

= lim

→0

= lim

−22 − 3

(−2 − 3)

−2 − 3

−3

= lim

= lim

=

(2 + 4 + 5) →0 (2 + 4 + 5) →0 2 + 4 + 5

5

N

→0

2

= lim

→0

So an equation of the tangent line at (2 2) is − 2 = − 3 ( − 2) or = − 3 +

5

5

16

.

5

27. Use (4) with () = 32 − 4 + 1.

( + ) − ()

[3( + )2 − 4( + ) + 1] − (32 − 4 + 1)]

= lim

→0

→0

0 () = lim

32 + 6 + 32 − 4 − 4 + 1 − 32 + 4 − 1

6 + 32 − 4

= lim

→0

→0

= lim

= lim

→0

(6 + 3 − 4)

= lim (6 + 3 − 4) = 6 − 4

→0

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

55

56

¤

CHAPTER 2

DERIVATIVES

29. Use (4) with () = (2 + 1)( + 3).

2( + ) + 1 2 + 1

−

( + ) − ()

( + ) + 3

+3

(2 + 2 + 1)( + 3) − (2 + 1)( + + 3)

0 () = lim

= lim

= lim

→0

→0

→0

( + + 3)( + 3)

= lim

(22 + 6 + 2 + 6 + + 3) − (22 + 2 + 6 + + + 3)

( + + 3)( + 3)

= lim

5

5

5

= lim

=

( + + 3)( + 3) →0 ( + + 3)( + 3)

( + 3)2

→0

→0

31. Use (4) with () =

√

1 − 2.

( + ) − ()

() = lim

= lim

→0

→0

0

√

1 − 2( + ) − 1 − 2

→0

(1 − 2 − 2) − (1 − 2)

−2

= lim

√

√

→0

1 − 2( + ) + 1 − 2

1 − 2( + ) + 1 − 2

rS

= lim

al

e

2 √

2

√

√

1 − 2( + ) −

1 − 2

1 − 2( + ) − 1 − 2

1 − 2( + ) + 1 − 2

= lim

·

= lim

√

√

→0

1 − 2( + ) + 1 − 2 →0

1 − 2( + ) + 1 − 2

−2

−2

−2

−1

√

= lim

= √

= √

= √

√

→0

1 − 2 + 1 − 2

2 1 − 2

1 − 2

1 − 2( + ) + 1 − 2

Fo

Note that the answers to Exercises 33 – 38 are not unique.

(1 + )10 − 1

= 0 (1), where () = 10 and = 1.

→0

33. By (4), lim

→0

(1 + )10 − 1

= 0 (0), where () = (1 + )10 and = 0.

ot

Or: By (4), lim

2 − 32

= 0 (5), where () = 2 and = 5.

→5 − 5

35. By Equation 5, lim

→0

cos( + ) + 1

= 0 (), where () = cos and = .

Or: By (4), lim

→0

N

37. By (4), lim

cos( + ) + 1

= 0 (0), where () = cos( + ) and = 0.

(5 + ) − (5)

[100 + 50(5 + ) − 49(5 + )2 ] − [100 + 50(5) − 49(5)2 ]

= lim

→0

(100 + 250 + 50 − 492 − 49 − 1225) − (100 + 250 − 1225)

−492 +

= lim

= lim

→0

→0

(−49 + 1)

= lim

= lim (−49 + 1) = 1 ms

→0

→0

39. (5) = 0 (5) = lim

→0

The speed when = 5 is |1| = 1 ms.

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

SECTION 2.1

DERIVATIVES AND RATES OF CHANGE

¤

57

41. The sketch shows the graph for a room temperature of 72◦ and a refrigerator

temperature of 38◦ . The initial rate of change is greater in magnitude than the rate of change after an hour.

43. (a) (i) [2002 2006]:

233 − 141

92

(2006) − (2002)

=

=

= 23 millions of cell phone subscribers per year

2006 − 2002

4

4

(ii) [2002 2004]:

(2004) − (2002)

182 − 141

41

=

=

= 205 millions of cell phone subscribers per year

2004 − 2002

2

2

(iii) [2000 2002]:

141 − 109

32

(2002) − (2000)

=

=

= 16 millions of cell phone subscribers per year

2002 − 2000

2

2

205 + 16

= 1825 millions of cell phone subscribers per year.

2

e

(b) Using the values from (ii) and (iii), we have

175 − 107

68

=

= 17 millions of cell phone subscribers per

2004 − 2000

4

rS

is

al

(c) Estimating A as (2000 107) and B as (2004 175), the slope at 2002

45. (a) (i)

Fo

year.

(105) − (100)

660125 − 6500

∆

=

=

= $2025unit.

∆

105 − 100

5

N

ot

(101) − (100)

652005 − 6500

∆

=

=

= $2005unit.

∆

101 − 100

1

5000 + 10(100 + ) + 005(100 + )2 − 6500

20 + 0052

(100 + ) − (100)

=

=

(b)

= 20 + 005, 6= 0

(ii)

So the instantaneous rate of change is lim

→0

(100 + ) − (100)

= lim (20 + 005) = $20unit.

→0

47. (a) 0 () is the rate of change of the production cost with respect to the number of ounces of gold produced. Its units are

dollars per ounce.

(b) After 800 ounces of gold have been produced, the rate at which the production cost is increasing is $17ounce. So the cost of producing the 800th (or 801st) ounce is about $17.

(c) In the short term, the values of 0 () will decrease because more efﬁcient use is made of start-up costs as increases. But eventually 0 () might increase due to large-scale operations.

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

58

¤

CHAPTER 2

DERIVATIVES

49. 0 (8) is the rate at which the temperature is changing at 8:00 AM . To estimate the value of 0 (8), we will average the

difference quotients obtained using the times = 6 and = 10.

Let =

75 − 84

(10) − (8)

90 − 84

(6) − (8)

=

= 45 and =

=

= 3. Then

6−8

−2

10 − 8

2

0 (8) = lim

→8

() − (8)

+

45 + 3

≈

=

= 375◦ Fh.

−8

2

2

51. (a) 0 ( ) is the rate at which the oxygen solubility changes with respect to the water temperature. Its units are (mgL)◦ C.

(b) For = 16◦ C, it appears that the tangent line to the curve goes through the points (0 14) and (32 6). So

6 − 14

8

=−

= −025 (mgL)◦ C. This means that as the temperature increases past 16◦ C, the oxygen

32 − 0

32

0 (16) ≈

e

solubility is decreasing at a rate of 025 (mgL)◦ C.

0 (0) = lim

→0

al

53. Since () = sin(1) when 6= 0 and (0) = 0, we have

(0 + ) − (0)

sin(1) − 0

= lim

= lim sin(1). This limit does not exist since sin(1) takes the

→0

→0

rS

values −1 and 1 on any interval containing 0. (Compare with Example 4 in Section 1.5.)

Fo

2.2 The Derivative as a Function

1. It appears that is an odd function, so 0 will be an even function—that

is, 0 (−) = 0 ().

(a) 0 (−3) ≈ −02

(c) 0 (−1) ≈ 1

(d) 0 (0) ≈ 2

(e) 0 (1) ≈ 1

(f) 0 (2) ≈ 0

(g) 0 (3) ≈ −02

N

ot

(b) 0 (−2) ≈ 0

3. (a)0 = II, since from left to right, the slopes of the tangents to graph (a) start out negative, become 0, then positive, then 0, then

negative again. The actual function values in graph II follow the same pattern.

(b)0 = IV, since from left to right, the slopes of the tangents to graph (b) start out at a ﬁxed positive quantity, then suddenly become negative, then positive again. The discontinuities in graph IV indicate sudden changes in the slopes of the tangents.

(c)0 = I, since the slopes of the tangents to graph (c) are negative for 0 and positive for 0, as are the function values of graph I.

(d)0 = III, since from left to right, the slopes of the tangents to graph (d) are positive, then 0, then negative, then 0, then positive, then 0, then negative again, and the function values in graph III follow the same pattern.

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

SECTION 2.2

THE DERIVATIVE AS A FUNCTION

¤

Hints for Exercises 4 –11: First plot -intercepts on the graph of 0 for any horizontal tangents on the graph of . Look for any corners on the graph of — there will be a discontinuity on the graph of 0 . On any interval where has a tangent with positive (or negative) slope, the graph of 0 will be positive (or negative). If the graph of the function is linear, the graph of 0 will be a horizontal line.

5.

al

e

7.

11.

ot

Fo

rS

9.

N

13. (a) 0 () is the instantaneous rate of change of percentage

of full capacity with respect to elapsed time in hours.

(b) The graph of 0 () tells us that the rate of change of percentage of full capacity is decreasing and approaching 0.

15. It appears that there are horizontal tangents on the graph of for = 1963

and = 1971. Thus, there are zeros for those values of on the graph of

0 . The derivative is negative for the years 1963 to 1971.

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

59

60

¤

CHAPTER 2

DERIVATIVES

17. (a) By zooming in, we estimate that 0 (0) = 0, 0

and 0 (2) = 4.

1

2

= 1, 0 (1) = 2,

(b) By symmetry, 0 (−) = − 0 (). So 0 − 1 = −1, 0 (−1) = −2,

2

and 0 (−2) = −4.

(c) It appears that 0 () is twice the value of , so we guess that 0 () = 2.

( + ) − ()

( + )2 − 2

= lim

→0

→0

2

+ 2 + 2 − 2

(2 + )

2 + 2

= lim

= lim

= lim

= lim (2 + ) = 2

→0

→0

→0

→0

(d) 0 () = lim

( + ) − ()

= lim

19. () = lim

→0

→0

0

→0

1

→0 2

= lim

=

2

( + ) −

1

3

−

1

2

−

1

3

= lim

1

2

→0

1

2

+ 1 − 1 − 1 +

2

3

2

1

3

e

= lim

1

2

1

al

Domain of = domain of 0 = R.

5( + ) − 9( + )2 − (5 − 92 )

( + ) − ()

= lim

→0

→0

rS

21. 0 () = lim

5 + 5 − 9(2 + 2 + 2 ) − 5 + 92

5 + 5 − 92 − 18 − 92 − 5 + 92

= lim

→0

→0

= lim

5 − 18 − 92

(5 − 18 − 9)

= lim

= lim (5 − 18 − 9) = 5 − 18

→0

→0

→0

Domain of = domain of 0 = R.

→0

= lim

→0

( + ) − ()

[( + )2 − 2( + )3 ] − (2 − 23 )

= lim

→0

ot

23. 0 () = lim

Fo

= lim

2 + 2 + 2 − 23 − 62 − 62 − 23 − 2 + 23

→0

N

2 + 2 − 62 − 62 − 23

(2 + − 62 − 6 − 22 )

= lim

→0

→0

= lim (2 + − 62 − 6 − 22 ) = 2 − 62

= lim

Domain of = domain of 0 = R.

( + ) − ()

= lim

25. () = lim

→0

→0

0

= lim

→0

√

√

9 − ( + ) − 9 −

9 − ( + ) + 9 −

√

9 − ( + ) + 9 −

[9 − ( + )] − (9 − )

−

= lim

√

√

→0

9 − ( + ) + 9 −

9 − ( + ) + 9 −

−1

−1

= √

= lim

√

→0

2 9−

9 − ( + ) + 9 −

Domain of = (−∞ 9], domain of 0 = (−∞ 9).

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

SECTION 2.2

THE DERIVATIVE AS A FUNCTION

¤

61

1 − 2( + )

1 − 2

−

( + ) − ()

3 + ( + )

3+

= lim

27. 0 () = lim

→0

→0

[1 − 2( + )](3 + ) − [3 + ( + )](1 − 2)

[3 + ( + )](3 + )

= lim

→0

3 + − 6 − 22 − 6 − 2 − (3 − 6 + − 22 + − 2)

−6 −

= lim

→0

→0 (3 + + )(3 + )

[3 + ( + )](3 + )

= lim

= lim

→0

−7

−7

−7

= lim

=

(3 + + )(3 + ) →0 (3 + + )(3 + )

(3 + )2

Domain of = domain of 0 = (−∞ −3) ∪ (−3 ∞).

4

+ 43 + 62 2 + 43 + 4 − 4

( + ) − ()

( + )4 − 4

= lim

= lim

29. () = lim

→0

→0

→0

3

2 2

3

4

3

4 + 6 + 4 +

= lim

= lim 4 + 62 + 42 + 3 = 43

→0

→0

e

0

→0

( + ) − ()

[( + )4 + 2( + )] − (4 + 2)

= lim

→0

rS

31. (a) 0 () = lim

al

Domain of = domain of 0 = R.

= lim

4 + 43 + 62 2 + 43 + 4 + 2 + 2 − 4 − 2

= lim

43 + 62 2 + 43 + 4 + 2

(43 + 62 + 42 + 3 + 2)

= lim

→0

→0

→0

Fo

= lim (43 + 62 + 42 + 3 + 2) = 43 + 2

→0

(b) Notice that 0 () = 0 when has a horizontal tangent, 0 () is positive when the tangents have positive slope, and 0 () is

N

ot

negative when the tangents have negative slope.

33. (a) 0 () is the rate at which the unemployment rate is changing with respect to time. Its units are percent per year.

(b) To ﬁnd 0 (), we use lim

→0

For 1999: 0 (1999) ≈

( + ) − ()

( + ) − ()

≈

for small values of .

40 − 42

(2000) − (1999)

=

= −02

2000 − 1999

1

For 2000: We estimate 0 (2000) by using = −1 and = 1, and then average the two results to obtain a ﬁnal estimate.

= −1 ⇒ 0 (2000) ≈

= 1 ⇒ 0 (2000) ≈

42 − 40

(1999) − (2000)

=

= −02;

1999 − 2000

−1

47 − 40

(2001) − (2000)

=

= 07.

2001 − 2000

1

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

[continued]

62

¤

CHAPTER 2

DERIVATIVES

So we estimate that 0 (2000) ≈ 1 [(−02) + 07] = 025.

2

1999

2000

2001

2002

2003

2004

2005

2006

2007

2008

0 ()

−02

025

09

065

−015

−045

−045

−025

06

12

35. is not differentiable at = −4, because the graph has a corner there, and at = 0, because there is a discontinuity there.

37. is not differentiable at = −1, because the graph has a vertical tangent there, and at = 4, because the graph has a corner

there.

39. As we zoom in toward (−1 0), the curve appears more and more like a straight

line, so () = +

|| is differentiable at = −1. But no matter how much

we zoom in toward the origin, the curve doesn’t straighten out—we can’t

e

eliminate the sharp point (a cusp). So is not differentiable at = 0.

al

41. = , = 0 , = 00 . We can see this because where has a horizontal tangent, = 0, and where has a horizontal tangent,

= 0. We can immediately see that can be neither nor 0 , since at the points where has a horizontal tangent, neither

rS

nor is equal to 0.

43. We can immediately see that is the graph of the acceleration function, since at the points where has a horizontal tangent,

neither nor is equal to 0. Next, we note that = 0 at the point where has a horizontal tangent, so must be the graph of

45. 0 () = lim

→0

Fo

the velocity function, and hence, 0 = . We conclude that is the graph of the position function.

( + ) − ()

[3( + )2 + 2( + ) + 1] − (32 + 2 + 1)

= lim

→0

(32 + 6 + 32 + 2 + 2 + 1) − (32 + 2 + 1)

6 + 32 + 2

= lim

→0

= lim

(6 + 3 + 2)

= lim (6 + 3 + 2) = 6 + 2

→0

→0

→0

ot

= lim

= lim

→0

N

0 ( + ) − 0 ()

[6( + ) + 2] − (6 + 2)

(6 + 6 + 2) − (6 + 2)

= lim

= lim

→0

→0

→0

00 () = lim

6

= lim 6 = 6

→0

We see from the graph that our answers are reasonable because the graph of

0 is that of a linear function and the graph of 00 is that of a constant function.

2( + )2 − ( + )3 − (22 − 3 )

( + ) − ()

= lim

→0

→0

47. 0 () = lim

(4 + 2 − 32 − 3 − 2 )

= lim (4 + 2 − 32 − 3 − 2 ) = 4 − 32

→0

→0

= lim

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

SECTION 2.2

THE DERIVATIVE AS A FUNCTION

¤

63

4( + ) − 3( + )2 − (4 − 32 )

0 ( + ) − 0 ()

(4 − 6 − 3)

= lim

= lim

00 () = lim

→0

→0

→0

= lim (4 − 6 − 3) = 4 − 6

→0

00 ( + ) − 00 ()

[4 − 6( + )] − (4 − 6)

−6

= lim

= lim

= lim (−6) = −6

→0

→0

→0

→0

000 () = lim

(4) () = lim

→0

000 ( + ) − 000 ()

−6 − (−6)

0

= lim

= lim = lim (0) = 0

→0

→0

→0

The graphs are consistent with the geometric interpretations of the derivatives because 0 has zeros where has a local minimum and a local maximum, 00 has a zero where 0 has a local maximum, and 000 is a

e

constant function equal to the slope of 00 .

= lim

→

(b) 0(0) = lim

→0

rS

→

() − ()

13 − 13

13 − 13

= lim

= lim 13

13 )(23 + 13 13 + 23 )

→

→ (

−

−

−

1

1

= 23 or 1 −23

3

23 + 13 13 + 23

3

(0 + ) − (0)

= lim

→0

√

3

−0

1

= lim 23 . This function increases without bound, so the limit does not

→0

Fo

0() = lim

al

49. (a) Note that we have factored − as the difference of two cubes in the third step.

exist, and therefore 0(0) does not exist.

(c) lim | 0 ()| = lim

→0

1

= ∞ and is continuous at = 0 (root function), so has a vertical tangent at = 0.

323

−6

ot

→0

−( − 6) if − 6 0

N

51. () = | − 6| =

So the right-hand limit is lim

→6+

is lim

→6−

if − 6 ≥ 6

=

− 6 if ≥ 6

6 − if 6

() − (6)

| − 6| − 0

−6

= lim

= lim

= lim 1 = 1, and the left-hand limit

−6

−6

→6+

→6+ − 6

→6+

() − (6)

| − 6| − 0

6−

= lim

= lim

= lim (−1) = −1. Since these limits are not equal,

−6

−6

→6−

→6− − 6

→6−

() − (6) does not exist and is not differentiable at 6.

−6

1

if 6

0

0

However, a formula for is () =

−1 if 6

0 (6) = lim

→6

Another way of writing the formula is 0 () =

−6

.

| − 6|

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

64

¤

CHAPTER 2 DERIVATIVES

53. (a) () = || =

2

if ≥ 0

(b) Since () = 2 for ≥ 0, we have 0 () = 2 for 0.

if 0

2

−

[See Exercise 17(d).] Similarly, since () = −2 for 0, we have 0 () = −2 for 0. At = 0, we have

0 (0) = lim

→0

() − (0)

||

= lim

= lim || = 0

→0

→0

−0

So is differentiable at 0. Thus, is differentiable for all .

(c) From part (b), we have () =

0

2 if ≥ 0

−2 if 0

= 2 ||.

55. (a) If is even, then

(− + ) − (−)

[−( − )] − (−)

= lim

→0

0 (−) = lim

e

→0

→0

= − lim

∆→0

( + ∆) − ()

= − 0 ()

∆

rS

Therefore, 0 is odd.

(b) If is odd, then

(− + ) − (−)

[−( − )] − (−)

= lim

→0

0 (−) = lim

→0

→0

= lim

∆→0

Fo

−( − ) + ()

( − ) − ()

= lim

→0

−

= lim

[let ∆ = −]

( + ∆) − ()

= 0 ()

∆

ot

Therefore, 0 is even.

[let ∆ = −]

al

( − ) − ()

( − ) − ()

= − lim

→0

−

= lim

In the right triangle in the diagram, let ∆ be the side opposite angle and ∆

57.

N

the side adjacent to angle . Then the slope of the tangent line is = ∆∆ = tan . Note that 0

2.

We know (see Exercise 17)

that the derivative of () = 2 is 0 () = 2. So the slope of the tangent to the curve at the point (1 1) is 2. Thus, is the angle between 0 and

2

tangent is 2; that is, = tan−1 2 ≈ 63◦ .

2.3 Differentiation Formulas

1. () = 240 is a constant function, so its derivative is 0, that is, 0 () = 0.

3. () = 2 − 2

3

⇒ 0 () = 0 −

5. () = 3 − 4 + 6

2

3

= −2

3

⇒ 0 () = 32 − 4(1) + 0 = 32 − 4

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

whose

SECTION 2.3 DIFFERENTIATION FORMULAS

7. () = 2 (1 − 2) = 2 − 23

9. () = 2−34

11. () = −

13. () =

⇒

65

⇒ 0 () = 2 − 2(32 ) = 2 − 62

0 () = 2(− 3 −74 ) = − 3 −74

4

2

12

= −12−5

5

⇒ 0 () = −12(−5−6 ) = 60−6

⇒ 0 () = 9(2) + 6(1) + 0 = 18 + 6

2 + 4 + 3

√

= 32 + 412 + 3−12

⇒

0 = 3 12 + 4 1 −12 + 3 − 1 −32 =

2

2

2

√ note that 32 = 22 · 12 =

√

2

3

√

+ √ −

2

e

3

2

32

4

3

32 + 4 − 3

√ +

√ −

√ =

√

.

2

2

2

2

al

The last expression can be written as

or 606

1

√ −1

2

√

− = 12 − ⇒ 0 () = 1 −12 − 1 or

2

15. () = (3 + 1)2 = 92 + 6 + 1

17. =

¤

19. We ﬁrst expand using the Binomial Theorem (see Reference Page 1).

0

−2

2

() = 3 + 3 + 3(−1

) + (−3

√

√

5

+ 4 5 = 15 + 452

2

) = 3 + 3 − 3

−2

− 3

⇒ 0 = 1 −45 + 4 5 32 = 1 −45 + 1032

5

2

5

23. Product Rule: () = (1 + 22 )( − 2 )

⇒

−4

Fo

21. =

−4

rS

() = ( + −1 )3 = 3 + 32 −1 + 3(−1 )2 + (−1 )3 = 3 + 3 + 3−1 + −3

√

√

5 or 1 5 4 + 10 3

⇒

0 () = (1 + 22 )(1 − 2) + ( − 2 )(4) = 1 − 2 + 22 − 43 + 42 − 43 = 1 − 2 + 62 − 83 .

ot

Multiplying ﬁrst: () = (1 + 22 )( − 2 ) = − 2 + 23 − 24

PR

⇒

N

25. () = (23 + 3)(4 − 2)

⇒ 0 () = 1 − 2 + 62 − 83 (equivalent).

0 () = (23 + 3)(43 − 2) + (4 − 2)(62 ) = (86 + 83 − 6) + (66 − 123 ) = 146 − 43 − 6

27. () =

1

3

PR

− 4 ( + 53 ) = ( −2 − 3 −4 )( + 5 3 ) ⇒

2

0 () = ( −2 − 3 −4 )(1 + 15 2 ) + ( + 53 )(−2 −3 + 12 −5 )

= ( −2 + 15 − 3 −4 − 45 −2 ) + (−2 −2 + 12 −4 − 10 + 60−2 )

= 5 + 14−2 + 9 −4 or 5 + 14 2 + 9 4

29. () =

31. =

1 + 2

3 − 4

3

1 − 2

QR

QR

⇒ 0 () =

⇒ 0 =

(3 − 4)(2) − (1 + 2)(−4)

6 − 8 + 4 + 8

10

=

=

(3 − 4)2

(3 − 4)2

(3 − 4)2

(1 − 2 ) (32 ) − 3 (−2)

2 (3 − 32 + 22 )

2 (3 − 2 )

=

=

(1 − 2 )2

(1 − 2 )2

(1 − 2 )2

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

66

¤

CHAPTER 2 DERIVATIVES

33. =

3 − 2

√

= 2 − 2

√

= 2 − 2 12

⇒ 0 = 2 − 2 1 −12 = 2 − −12 .

2

√

1

2 − 1

2 32 − 1

√

√

=

We can change the form of the answer as follows: 2 − −12 = 2 − √ =

=

QR

⇒

(4 − 32 + 1)(2) − (2 + 2)(43 − 6)

2[(4 − 32 + 1) − (2 + 2)(22 − 3)]

=

4 − 32 + 1)2

(

(4 − 32 + 1)2

2(4 − 32 + 1 − 24 − 42 + 32 + 6)

2(−4 − 42 + 7)

=

(4 − 32 + 1)2

(4 − 32 + 1)2

⇒ 0 = 2 +

37. = 2 + +

√

(2 + 12 )(2) − 2 1 −12

2

4 + 212 − 12

4 + 12

4+

√

√

√

√

⇒ 0 () =

=

= or (2 + )2

(2 + )2

(2 + )2

(2 + )2

2

√

39. () =

2+

41. =

e

0 =

2 + 2

4 − 32 + 1

QR

√ 2

3

( + + −1 ) = 13 (2 + + −1 ) = 73 + 43 + −23

al

35. =

⇒

+

⇒ 0 () =

( + )(1) − (1 − 2 )

+ − +

2

2

2

=

=

2

2

2

2

2 · 2 =

(2 + )2

( + )

+

+

2

Fo

43. () =

rS

0 = 7 43 + 4 13 − 2 −53 = 1 −53 (793 + 463 − 2) = (73 + 42 − 2)(353 )

3

3

3

3

45. () = + −1 −1 + · · · + 2 2 + 1 + 0

⇒ 0 () = 4514 − 152 .

ot

47. () = 315 − 53 + 3

⇒ 0 () = −1 + ( − 1)−1 −2 + · · · + 22 + 1

Notice that 0 () = 0 when has a horizontal tangent, 0 is positive

49. (a)

N

when is increasing, and 0 is negative when is decreasing.

(b) From the graph in part (a), it appears that 0 is zero at 1 ≈ −125, 2 ≈ 05, and 3 ≈ 3. The slopes are negative (so 0 is negative) on (−∞ 1 ) and

(2 3 ). The slopes are positive (so 0 is positive) on (1 2 ) and (3 ∞).

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

SECTION 2.3 DIFFERENTIATION FORMULAS

¤

(c) () = 4 − 33 − 62 + 7 + 30 ⇒

0 () = 43 − 92 − 12 + 7

51. =

2

+1

⇒ 0 =

( + 1)(2) − (2)(1)

2

=

.

( + 1)2

( + 1)2

At (1 1), 0 = 1 , and an equation of the tangent line is − 1 = 1 ( − 1), or = 1 + 1 .

2

2

2

2

(b)

⇒

(1 + 2 )(0) − 1(2)

−2

=

. So the slope of the

(1 + 2 )2

(1 + 2 )2

2 tangent line at the point −1 1 is 0 (−1) = 2 =

2

2

equation is −

1

2

= 1 ( + 1) or = 1 + 1.

2

2

1

2

and its

al

0 () =

1

1 + 2

e

53. (a) = () =

rS

√

√

⇒ 0 = 1 + 1 −12 = 1 + 1(2 ) . At (1 2), 0 = 3 , and an equation of the tangent line is

2

2

55. = +

− 2 = 3 ( − 1), or = 3 + 1 . The slope of the normal line is − 2 , so an equation of the normal line is

2

2

2

3

57. =

3 + 1

2 + 1

⇒ 0 =

Fo

− 2 = − 2 ( − 1), or = − 2 + 8 .

3

3

3

(2 + 1)(3) − (3 + 1)(2)

6−8

1

. At (1 2), 0 =

= − , and an equation of the tangent line

(2 + 1)2

22

2

is − 2 = − 1 ( − 1), or = − 1 + 5 . The slope of the normal line is 2, so an equation of the normal line is

2

2

2

ot

− 2 = 2( − 1), or = 2.

⇒ 0 () = 43 − 92 + 16 ⇒ 00 () = 122 − 18

N

59. () = 4 − 33 + 16

61. () =

2

1 + 2

00 () =

=

⇒ 0 () =

(1 + 2)(2) − 2 (2)

2 + 42 − 22

22 + 2

=

=

(1 + 2)2

(1 + 2)2

(1 + 2)2

⇒

(1 + 2)2 (4 + 2) − (22 + 2)(1 + 4 + 42 )0

2(1 + 2)2 (2 + 1) − 2( + 1)(4 + 8)

=

2 ]2

[(1 + 2)

(1 + 2)4

2(1 + 2)[(1 + 2)2 − 4( + 1)]

2(1 + 4 + 42 − 42 − 4)

2

=

=

(1 + 2)4

(1 + 2)3

(1 + 2)3

63. (a) = 3 − 3

⇒ () = 0 () = 32 − 3 ⇒ () = 0 () = 6

(b) (2) = 6(2) = 12 ms2

(c) () = 32 − 3 = 0 when 2 = 1, that is, = 1 [ ≥ 0] and (1) = 6 ms2 .

65. (a) =

53

53

and = 50 when = 0106, so = = 50(0106) = 53. Thus, = and =

.

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

67

68

¤

CHAPTER 2 DERIVATIVES

(b) = 53 −1

⇒

53

53

= 53(−1 −2 ) = − 2 . When = 50,

= − 2 = −000212. The derivative is the

50

instantaneous rate of change of the volume with respect to the pressure at 25 ◦ C. Its units are m3kPa.

67. We are given that (5) = 1, 0 (5) = 6, (5) = −3, and 0 (5) = 2.

(a) ( )0 (5) = (5) 0 (5) + (5) 0 (5) = (1)(2) + (−3)(6) = 2 − 18 = −16

0

(5) 0 (5) − (5)0 (5)

(−3)(6) − (1)(2)

20

(b)

(5) =

=

=−

[(5)]2

(−3)2

9

(c)

0

(5) 0 (5) − (5) 0 (5)

(1)(2) − (−3)(6)

(5) =

=

= 20

[ (5)]2

(1)2

69. () =

√

√

√

1

1

1

() ⇒ 0 () = 0 () + () · −12 , so 0 (4) = 4 0 (4) + (4) · √ = 2 · 7 + 8 · = 16.

2

4

2 4

e

71. (a) From the graphs of and , we obtain the following values: (1) = 2 since the point (1 2) is on the graph of ;

(2 4) is

al

(1) = 1 since the point (1 1) is on the graph of ; 0 (1) = 2 since the slope of the line segment between (0 0) and

0−4

4−0

= 2; 0 (1) = −1 since the slope of the line segment between (−2 4) and (2 0) is

= −1.

2−0

2 − (−2)

⇒

0 = 0 () + () · 1 = 0 () + ()

Fo

73. (a) = ()

rS

Now () = ()(), so 0 (1) = (1)0 (1) + (1) 0 (1) = 2 · (−1) + 1 · 2 = 0.

2 −1 − 3 · 2

−8

2

(5) 0 (5) − (5)0 (5)

3

3

=

= 3 =−

(b) () = ()(), so 0 (5) =

2

2

[(5)]

2

4

3

()

⇒ 0 =

() · 1 − 0 ()

() − 0 ()

=

[()]2

[()]2

(c) =

()

⇒ 0 =

0 () − () · 1

0 () − ()

=

()2

2

ot

(b) =

75. The curve = 23 + 32 − 12 + 1 has a horizontal tangent when 0 = 62 + 6 − 12 = 0

⇔ 6(2 + − 2) = 0 ⇔

N

6( + 2)( − 1) = 0 ⇔ = −2 or = 1. The points on the curve are (−2 21) and (1 −6).

77. = 63 + 5 − 3

⇒ = 0 = 182 + 5, but 2 ≥ 0 for all , so ≥ 5 for all .

79. The slope of the line 12 − = 1 (or = 12 − 1) is 12, so the slope of both lines tangent to the curve is 12.

= 1 + 3

⇒ 0 = 32 . Thus, 32 = 12 ⇒ 2 = 4 ⇒ = ±2, which are the -coordinates at which the tangent

lines have slope 12. The points on the curve are (2 9) and (−2 −7), so the tangent line equations are − 9 = 12( − 2) or = 12 − 15 and + 7 = 12( + 2) or = 12 + 17.

81. The slope of = 2 − 5 + 4 is given by = 0 = 2 − 5. The slope of − 3 = 5

⇔ = 1 −

3

5

3

is 1 ,

3

so the desired normal line must have slope 1 , and hence, the tangent line to the parabola must have slope −3. This occurs if

3

2 − 5 = −3 ⇒ 2 = 2 ⇒ = 1. When = 1, = 12 − 5(1) + 4 = 0, and an equation of the normal line is

− 0 = 1 ( − 1) or = 1 − 1 .

3

3

3

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

SECTION 2.3 DIFFERENTIATION FORMULAS

¤

Let 2 be a point on the parabola at which the tangent line passes

83.

through the point (0 −4). The tangent line has slope 2 and equation

− (−4) = 2( − 0) ⇔ = 2 − 4. Since 2 also lies on the

line, 2 = 2() − 4, or 2 = 4. So = ±2 and the points are (2 4) and (−2 4).

85. (a) ( )0 = [()]0 = ( )0 + ( )0 = ( 0 + 0 ) + ( )0 = 0 + 0 + 0

(b) Putting = = in part (a), we have

(c) = (4 + 33 + 17 + 82)3

[ ()]3 = ( )0 = 0 + 0 + 0 = 3 0 = 3[()]2 0 ().

⇒ 0 = 3(4 + 33 + 17 + 82)2 (43 + 92 + 17)

al

0 (2) = 3 ⇒ 2(1)(2) + = 3 ⇒ 4 + = 3 ⇒ = −1.

⇒ 2 = 2 ⇒ = 1.

e

87. Let () = 2 + + . Then 0 () = 2 + and 00 () = 2. 00 (2) = 2

(2) = 5 ⇒ 1(2)2 + (−1)(2) + = 5 ⇒ 2 + = 5 ⇒ = 3. So () = 2 − + 3.

⇒ 0 () = 32 + 2 + . The point (−2 6) is on , so (−2) = 6 ⇒

rS

89. = () = 3 + 2 + +

−8 + 4 − 2 + = 6 (1). The point (2 0) is on , so (2) = 0 ⇒ 8 + 4 + 2 + = 0 (2). Since there are horizontal tangents at (−2 6) and (2 0), 0 (±2) = 0. 0 (−2) = 0 ⇒ 12 − 4 + = 0 (3) and 0 (2) = 0 ⇒

Fo

12 + 4 + = 0 (4). Subtracting equation (3) from (4) gives 8 = 0 ⇒ = 0. Adding (1) and (2) gives 8 + 2 = 6, so = 3 since = 0. From (3) we have = −12, so (2) becomes 8 + 4(0) + 2(−12) + 3 = 0 ⇒ 3 = 16 ⇒

3

3

3

= 16 . Now = −12 = −12 16 = − 9 and the desired cubic function is = 16 3 − 9 + 3.

4

4

ot

91. If () denotes the population at time and () the average annual income, then () = ()() is the total personal

income. The rate at which () is rising is given by 0 () = ()0 () + () 0 () ⇒

N

0 (1999) = (1999)0 (1999) + (1999) 0 (1999) = (961,400)($1400yr) + ($30,593)(9200yr)

= $1,345,960,000yr + $281,455,600yr = $1,627,415,600yr

So the total personal income was rising by about $1.627 billion per year in 1999.

The term ()0 () ≈ $1.346 billion represents the portion of the rate of change of total income due to the existing population’s increasing income. The term () 0 () ≈ $281 million represents the portion of the rate of change of total income due to increasing population.

93. () =

2 + 1

if 1

+1

if ≥ 1

Calculate the left- and right-hand derivatives as deﬁned in Exercise 2.2.54:

0

− (1) = lim

→0−

(1 + ) − (1)

[(1 + )2 + 1] − (1 + 1)

2 + 2

= lim

= lim

= lim ( + 2) = 2 and

−

−

→0

→0

→0−

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

69

70

¤

CHAPTER 2 DERIVATIVES

0

+ (1) = lim

→0+

(1 + ) − (1)

[(1 + ) + 1] − (1 + 1)

= lim

= lim

= lim 1 = 1.

+

+

→0

→0

→0+

Since the left and right limits are different, lim →0

(1 + ) − (1) does not exist, that is, 0 (1)

does not exist. Therefore, is not differentiable at 1.

2

−9

() =

−2 + 9

2

−9

⇔ || 3 ⇔ −3 3. So

if ≤ −3

if −3 3 if ≥ 3

2

0

−2

⇒ () =

2

To show that 0 (3) does not exist we investigate lim

→0

if −3

if −3 3 if 3

=

2

−2

if || 3

if || 3

(3 + ) − (3) by computing the left- and right-hand derivatives

al

deﬁned in Exercise 2.2.54.

e

95. (a) Note that 2 − 9 0 for 2 9

(3 + ) − (3)

[−(3 + )2 + 9] − 0

= lim

= lim (−6 − ) = −6 and

−

→0

→0−

(3 + )2 − 9 − 0

(3 + ) − (3)

6 + 2

0

= lim

= lim

= lim (6 + ) = 6.

+ (3) = lim

→0+

→0+

→0+

→0+

0

− (3) = lim

rS

→0−

Since the left and right limits are different,

Fo

lim

→0

(b)

(3 + ) − (3) does not exist, that is, 0 (3)

does not exist. Similarly, 0 (−3) does not exist.

⇒ 0 () = 2.

So the slope of the tangent to the parabola at = 2 is = 2(2) = 4. The slope

N

97. = () = 2

ot

Therefore, is not differentiable at 3 or at −3.

of the given line, 2 + = ⇔ = −2 + , is seen to be −2, so we must have 4 = −2 ⇔ = − 1 . So when

2

= 2, the point in question has -coordinate − 1 · 22 = −2. Now we simply require that the given line, whose equation is

2

2 + = , pass through the point (2 −2): 2(2) + (−2) = ⇔ = 2. So we must have = − 1 and = 2.

2

√

is 0 =

√ and the slope of the tangent line = 3 + 6 is 3 . These must be equal at the

2

2

√

√

3

point of tangency , so √ =

⇒ = 3 . The -coordinates must be equal at = , so

2

2

√ √

√

√

3

= 3 + 6 ⇒ 3 = 3 + 6 ⇒ 3 = 6 ⇒ = 4. Since = 3 , we have

= 3 + 6 ⇒

2

2

2

2

99. The slope of the curve =

=3

2

√

4 = 6.

101. =

⇒ =

⇒ 0 = 0 + 0

⇒ 0 =

0 − ( ) 0

0 − 0

0 − 0

=

=

2

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

SECTION 2.4 DERIVATIVES OF TRIGONOMETRIC FUNCTIONS

103. Solution 1:

Let () = 1000 . Then, by the deﬁnition of a derivative, 0 (1) = lim

→1

¤

71

() − (1)

1000 − 1

= lim

.

→1

−1

−1

But this is just the limit we want to ﬁnd, and we know (from the Power Rule) that 0 () = 1000999 , so

0 (1) = 1000(1)999 = 1000. So lim

→1

− 1) = ( − 1)(999 + 998 + 997 + · · · + 2 + + 1). So

1000

Solution 2: Note that ( lim →1

1000 − 1

= 1000.

−1

1000 − 1

( − 1)(999 + 998 + 997 + · · · + 2 + + 1)

= lim

= lim (999 + 998 + 997 + · · · + 2 + + 1)

→1

→1

−1

−1

= 1 + 1 + 1 + · · · + 1 + 1 + 1 = 1000, as above.

1000 ones

⇒ 0 = 2, so the slope of a tangent line at the point ( 2 ) is 0 = 2 and the slope of a normal line is −1(2),

105. = 2

2 −

1

2 −

, so

=−

−0

2

e

for 6= 0. The slope of the normal line through the points ( 2 ) and (0 ) is

⇒

al

⇒ 2 = − 1 . The last equation has two solutions if 1 , one solution if = 1 , and no solution if

2

2

2

2 − = − 1

2

if

and one normal line if ≤ 1 .

2

1

2

rS

1 . Since the -axis is normal to = 2 regardless of the value of (this is the case for = 0), we have three normal lines

2

1. () = 32 − 2 cos

3. () = sin +

1

2

⇒ 0 () = 6 − 2(− sin ) = 6 + 2 sin

cot ⇒ 0 () = cos −

1

2

csc2

⇒ 0 = sec (sec2 ) + tan (sec tan ) = sec (sec2 + tan2 ). Using the identity

ot

5. = sec tan

Fo

2.4 Derivatives of Trigonometric Functions

1 + tan2 = sec2 , we can write alternative forms of the answer as sec (1 + 2 tan2 ) or sec (2 sec2 − 1).

9. =

2 − tan

11. () =

sec

1 + sec

0 () =

13. =

0 =

⇒

0 = (− sin ) + 2 (cos ) + sin (2) = − sin + ( cos + 2 sin )

N

7. = cos + 2 sin

⇒ 0 =

(2 − tan )(1) − (− sec2 )

2 − tan + sec2

=

(2 − tan )2

(2 − tan )2

⇒

(1 + sec )(sec tan ) − (sec )(sec tan )

(sec tan ) [(1 + sec ) − sec ] sec tan

=

=

(1 + sec )2

(1 + sec )2

(1 + sec )2

sin

1+

⇒

(1 + )( cos + sin ) − sin (1)

cos + sin + 2 cos + sin − sin

(2 + ) cos + sin

=

=

(1 + )2

(1 + )2

(1 + )2

15. () = csc − cot

⇒ 0 () = (− csc cot ) + (csc ) · 1 − − csc2 = csc − csc cot + csc2

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

72

¤

17.

(csc ) =

19.

sin2 + cos2

1

cos (sin )(− sin ) − (cos )(cos )

=−

= − 2 = − csc2

(cot ) =

=

2

sin sin sin2 sin

CHAPTER 2 DERIVATIVES

1 sin

=

(sin )(0) − 1(cos )

− cos

1

cos

=

=−

·

= − csc cot sin sin sin2 sin2

√

⇒ 0 = sec tan , so 0 ( ) = sec tan = 2 3. An equation of the tangent line to the curve = sec

3

3

3

√

√

√

at the point 2 is − 2 = 2 3 − or = 2 3 + 2 − 2 3 .

3

3

3

21. = sec

23. = cos − sin

⇒ 0 = − sin − cos , so 0 () = − sin − cos = 0 − (−1) = 1. An equation of the tangent

line to the curve = cos − sin at the point ( −1) is − (−1) = 1( − ) or = − − 1.

⇒ 0 = 2( cos + sin · 1). At ,

2

0 = 2 cos + sin = 2(0 + 1) = 2, and an equation of the

2

2

2

tangent line is − = 2 − , or = 2.

2

(b)

al

27. (a) () = sec −

e

25. (a) = 2 sin

⇒ 0 () = sec tan − 1

rS

(b)

Note that 0 = 0 where has a minimum. Also note that 0 is negative

Fo

when is decreasing and 0 is positive when is increasing.

⇒ 0 () = (cos ) + (sin ) · 1 = cos + sin

29. () = sin

00

⇒

() = (− sin ) + (cos ) · 1 + cos = − sin + 2 cos

tan − 1

⇒

sec

2

1 + tan sec (sec ) − (tan − 1)(sec tan ) sec (sec2 − tan2 + tan )

0 () =

=

=

2

(sec ) sec 2 sec

N

ot

31. (a) () =

sin − cos sin

−1

tan − 1 cos cos

=

= sin − cos ⇒ 0 () = cos − (− sin ) = cos + sin

(b) () =

=

1

1

sec cos cos

1

tan

1 + tan

=

+

= cos + sin , which is the expression for 0 () in part (b).

(c) From part (a), 0 () = sec sec sec

33. () = + 2 sin has a horizontal tangent when 0 () = 0

=

2

3

+ 2 or

4

3

+ 2, where is an integer. Note that

⇔

4

3

and

1 + 2 cos = 0 ⇔ cos = − 1

2

2

3

⇔

are ± units from . This allows us to write the

3

solutions in the more compact equivalent form (2 + 1) ± , an integer.

3

⇒ () = 0 () = 8 cos ⇒ () = 00 () = −8 sin

√

√

(b) The mass at time = 2 has position 2 = 8 sin 2 = 8 23 = 4 3, velocity 2 = 8 cos 2 = 8 − 1 = −4,

3

3

3

3

3

2

35. (a) () = 8 sin

√

√

and acceleration 2 = −8 sin 2 = −8 23 = −4 3. Since 2 0, the particle is moving to the left.

3

3

3

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

SECTION 2.4 DERIVATIVES OF TRIGONOMETRIC FUNCTIONS

¤

73

From the diagram we can see that sin = 10 ⇔ = 10 sin . We want to ﬁnd the rate

37.

of change of with respect to , that is, . Taking the derivative of = 10 sin , we get

= 10(cos ). So when =

39. lim

→0

sin 3

3 sin 3

= lim

→0

3

sin 3

= 3 lim

3→0

3 sin

= 3 lim

→0

= 3(1)

,

3

= 10 cos = 10 1 = 5 ftrad.

3

2

[multiply numerator and denominator by 3]

[as → 0, 3 → 0]

[let = 3]

[Equation 2]

= 6 lim

→0

sin 6

1

·

·

cos 6 sin 2

sin 3

3

· 2

3

5 − 4

45. Divide numerator and denominator by .

6 sin 6

1

2

· lim

· lim

→0 cos 6 →0 2 sin 2

6

sin 3

3

= lim

· lim

= 1·

→0

→0 52 − 4

3

3

−4

=−

3

4

(sin also works.)

sin sin lim 1

1

→0

=

=

=

sin sin

1

1

1+1·1

2

1+

1 + lim

·

lim

→0

cos

→0 cos

ot

1 − tan

= lim sin − cos →4

sin

1−

· cos

√

cos cos − sin

−1

−1

= lim

= lim

= √ =− 2

(sin − cos ) · cos →4 (sin − cos ) cos →4 cos

1 2

(sin ) = cos ⇒

2

(sin ) = − sin ⇒

2

N

49.

lim

→0

Fo

sin lim = lim

→0 + tan

→0

→4

= lim

sin 6

1

2

1

1 1

· lim

· lim

= 6(1) · · (1) = 3

→0 cos 6

6

2 →0 sin 2

1 2

sin 3

= lim

43. lim

→0 53 − 4

→0

47.

al

→0

tan 6

= lim

→0

sin 2

rS

41. lim

e

=3

3

(sin ) = − cos ⇒

3

The derivatives of sin occur in a cycle of four. Since 99 = 4(24) + 3, we have

51. = sin + cos

4

(sin ) = sin .

4

99

3

(sin ) =

(sin ) = − cos .

99

3

⇒ 0 = cos − sin ⇒ 00 = − sin − cos . Substituting these

expressions for , 0 , and 00 into the given differential equation 00 + 0 − 2 = sin gives us

(− sin − cos ) + ( cos − sin ) − 2( sin + cos ) = sin ⇔

−3 sin − sin + cos − 3 cos = sin ⇔ (−3 − ) sin + ( − 3) cos = 1 sin , so we must have

−3 − = 1 and − 3 = 0 (since 0 is the coefﬁcient of cos on the right side). Solving for and , we add the ﬁrst

1

3 equation to three times the second to get = − 10 and = − 10 .

53. (a)

sin

tan =

cos

⇒ sec2 =

cos2 + sin2 cos cos − sin (− sin )

=

.

2

cos cos2

So sec2 =

1

.

cos2

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

74

¤

CHAPTER 2 DERIVATIVES

(b)

1 sec =

cos

(c)

1 + cot

(sin + cos ) =

csc cos − sin =

=

⇒ sec tan =

(cos )(0) − 1(− sin )

.

cos2

So sec tan =

sin

.

cos2

⇒

csc (− csc2 ) − (1 + cot )(− csc cot ) csc [− csc2 + (1 + cot ) cot ]

=

csc2 csc2

− csc2 + cot2 + cot

−1 + cot

=

csc csc

So cos − sin =

cot − 1

.

csc

55. By the deﬁnition of radian measure, = , where is the radius of the circle. By drawing the bisector of the angle , we can

2

=

2

2 · (2)

2

⇒ = 2 sin . So lim

= lim

= lim

= lim

= 1.

→0 sin(2)

2

→0+

→0+ 2 sin(2)

→0+ 2 sin(2)

[This is just the reciprocal of the limit lim

sin

= 1 combined with the fact that as → 0,

1. Let = () = 1 + 4 and = () =

√

4

3

. Then

.

=

= ( 1 −23 )(4) =

3

3 3 (1 + 4)2

5. Let = () = sin and = () =

√ cos

cos

.

=

= 1 −12 cos = √ = √

. Then

2

2 sin

2

⇒ 0 () = 5(4 + 32 − 2)4 ·

ot

7. () = (4 + 32 − 2)5

or 10(4 + 32 − 2)4 (22 + 3)

N

√

1 − 2 = (1 − 2)12

1

= ( 2 + 1)−1

2 + 1

13. = cos(3 + 3 )

=

= (sec2 )() = sec2 .

Fo

3. Let = () = and = () = tan . Then

11. () =

→ 0 also]

⇒

⇒

4

+ 32 − 2 = 5(4 + 32 − 2)4 (43 + 6)

1

0 () = 1 (1 − 2)−12 (−2) = − √

2

1 − 2

0 () = −1( 2 + 1)−2 (2) = −

⇒ 0 = − sin(3 + 3 ) · 32

15. Use the Product Rule.

rS

2.5 The Chain Rule

9. () =

2

al

→0

e

see that sin

2

( 2 + 1)2

[3 is just a constant] = −32 sin(3 + 3 )

= sec ⇒ 0 = (sec tan · ) + sec · 1 = sec ( tan + 1)

17. () = (2 − 3)4 (2 + + 1)5

⇒

0 () = (2 − 3)4 · 5(2 + + 1)4 (2 + 1) + (2 + + 1)5 · 4(2 − 3)3 · 2

= (2 − 3)3 (2 + + 1)4 [(2 − 3) · 5(2 + 1) + (2 + + 1) · 8]

= (2 − 3)3 (2 + + 1)4 (202 − 20 − 15 + 82 + 8 + 8) = (2 − 3)3 (2 + + 1)4 (282 − 12 − 7) c ° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

SECTION 2.5 THE CHAIN RULE

19. () = ( + 1)23 (22 − 1)3

¤

⇒

0 () = ( + 1)23 · 3(22 − 1)2 · 4 + (22 − 1)3 · 2 ( + 1)−13 = 2 ( + 1)−13 (22 − 1)2 [18( + 1) + (22 − 1)]

3

3

= 2 ( + 1)−13 (22 − 1)2 (202 + 18 − 1)

3

21. =

2 + 1

2 − 1

3

⇒

2

2

2

2

(2 − 1)(2) − (2 + 1)(2)

+1

2 + 1

+1

·

·

=3 2

=3 2

2 −1

−1

−1

(2 − 1)2

0

2

2

2

2

+1

2[2 − 1 − (2 + 1)]

+1

2(−2)

−12(2 + 1)2

=3 2

·

=3 2

· 2

=

2 − 1)2

2

−1

(

−1

( − 1)

(2 − 1)4

=

−1

+1

12

⇒

−12

12

1 +1

1 −1

−1

( + 1)(1) − ( − 1)(1)

=

·

·

2 +1

+ 1

2 −1

( + 1)2

al

0 () =

−1

=

+1

1 ( + 1)12 + 1 − + 1

1 ( + 1)12

2

1

·

=

·

=

2

12

2 ( − 1)

( + 1)

2 ( − 1)12 ( + 1)2

( − 1)12 ( + 1)32

2 + 1

27. = √

rS

25. () =

e

⇒ 0 = cos( cos ) · [(− sin ) + cos · 1] = (cos − sin ) cos( cos )

23. = sin( cos )

Fo

⇒

ot

√

2

√

2 + 1 − √

2 + 1 (1) − · 1 (2 + 1)−12 (2)

2 + 1

2

=

=

0 =

2

2

√

√

2 +1

2 +1

2

+ 1 − 2

1

= √ or (2 + 1)−32

3 = 2

2 +1

( + 1)32

√

√

2 + 1 2 + 1 − 2

√

2 + 1

2

√

2 + 1

N

Another solution: Write as a product and make use of the Product Rule. = (2 + 1)−12

⇒

0 = · − 1 (2 + 1)−32 (2) + (2 + 1)−12 · 1 = (2 + 1)−32 [−2 + (2 + 1)1 ] = (2 + 1)−32 (1) = (2 + 1)−32 .

2

The step that students usually have trouble with is factoring out (2 + 1)−32 . But this is no different than factoring out 2 from 2 + 5 ; that is, we are just factoring out a factor with the smallest exponent that appears on it. In this case, − 3 is

2

smaller than − 1 .

2

29. = sin

√

1 + 2

31. = sin(tan 2)

⇒ 0 = cos

√

√

√

1 + 2 · 1 (1 + 2 )−12 · 2 = cos 1 + 2 1 + 2

2

⇒ 0 = cos(tan 2) ·

(tan 2) = cos(tan 2) · sec2 (2) ·

(2) = 2 cos(tan 2) sec2 (2)

33. = sec2 + tan2 = (sec )2 + (tan )2

⇒

0 = 2(sec )(sec tan ) + 2(tan )(sec2 ) = 2 sec2 tan + 2 sec2 tan = 4 sec2 tan

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

75

76

¤

CHAPTER 2 DERIVATIVES

35. =

1 − cos 2

1 + cos 2

4

⇒

3

(1 + cos 2)(2 sin 2) + (1 − cos 2)(−2 sin 2)

1 − cos 2

=4

·

1 + cos 2

(1 + cos 2)2

3

1 − cos 2

2 sin 2 (1 + cos 2 + 1 − cos 2) 4(1 − cos 2)3 2 sin 2 (2)

16 sin 2 (1 − cos 2)3

=4

·

=

=

2

3 (1 + cos 2)2

1 + cos 2

(1 + cos 2)

(1 + cos 2)

(1 + cos 2)5

0

37. = cot2 (sin ) = [cot(sin )]2

0 = 2[cot(sin )] ·

⇒

[cot(sin )] = 2 cot(sin ) · [− csc2 (sin ) · cos ] = −2 cos cot(sin ) csc2 (sin )

39. = [2 + (1 − 3)5 ]3

⇒

0 = 3[2 + (1 − 3)5 ]2 (2 + 5(1 − 3)4 (−3)) = 3[2 + (1 − 3)5 ]2 [2 − 15(1 − 3)4 ]

43. () = (2 sin + )

45. = cos

( +

√ −12

)

1 + 1 −12 =

2

1

√

2 +

1+

e

1

2

1

√

2

al

√

+ ⇒ 0 =

⇒ 0 () = (2 sin + )−1 (2 cos · ) = (2 sin + )−1 (22 cos )

sin(tan ) = cos(sin(tan ))12

⇒

rS

41. =

(sin(tan ))12 = − sin(sin(tan ))12 · 1 (sin(tan ))−12 ·

(sin(tan ))

2

− sin sin(tan )

− sin sin(tan )

=

· cos(tan ) ·

· cos(tan ) · sec2 () · tan =

2 sin(tan )

2 sin(tan )

− cos(tan ) sec2 () sin sin(tan )

=

2 sin(tan )

47. = cos(2 )

⇒

ot

Fo

0 = − sin(sin(tan ))12 ·

0 = − sin(2 ) · 2 = −2 sin(2 )

⇒

49. () = tan 3

N

00 = −2 cos(2 ) · 2 + sin(2 ) · (−2) = −42 cos(2 ) − 2 sin(2 )

⇒ 0 () = 3 sec2 3 ⇒

00 () = 2 · 3 sec 3

51. = (1 + 2)10

(sec 3) = 6 sec 3 (3 sec 3 tan 3) = 18 sec2 3 tan 3

⇒ 0 = 10(1 + 2)9 · 2 = 20(1 + 2)9 .

At (0 1), 0 = 20(1 + 0)9 = 20, and an equation of the tangent line is − 1 = 20( − 0), or = 20 + 1.

53. = sin(sin )

⇒ 0 = cos(sin ) · cos . At ( 0), 0 = cos(sin ) · cos = cos(0) · (−1) = 1(−1) = −1, and an

equation of the tangent line is − 0 = −1( − ), or = − + .

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

SECTION 2.5 THE CHAIN RULE

55. (a) = () = tan

2

4

⇒ 0 () = sec2

2

4

The slope of the tangent at (1 1) is thus

0 (1) = sec2 = 2 · = , and its equation

4 2

2

2· 4 .

¤

77

(b)

is − 1 = ( − 1) or = − + 1.

57. (a) () =

√

2 − 2 = (2 − 2 )12

⇒

2 − 22

0 () = · 1 (2 − 2 )−12 (−2) + (2 − 2 )12 · 1 = (2 − 2 )−12 −2 + (2 − 2 ) = √

2

2 − 2

0 = 0 when has a horizontal tangent line, 0 is negative when is

(b)

e

decreasing, and 0 is positive when is increasing.

⇒ 0 () = 2 cos + 2 sin cos = 0 ⇔

al

59. For the tangent line to be horizontal, 0 () = 0. () = 2 sin + sin2

rS

2 cos (1 + sin ) = 0 ⇔ cos = 0 or sin = −1, so = + 2 or 3 + 2, where is any integer. Now

2

2

3

2 = 3 and 2 = −1, so the points on the curve with a horizontal tangent are + 2 3 and 3 + 2 −1 ,

2

2 where is any integer.

⇒ 0 () = 0 (()) · 0 (), so 0 (5) = 0 ((5)) · 0 (5) = 0 (−2) · 6 = 4 · 6 = 24

63. (a) () = (())

Fo

61. () = (())

⇒ 0 () = 0 (()) · 0 (), so 0 (1) = 0 ((1)) · 0 (1) = 0 (2) · 6 = 5 · 6 = 30.

(b) () = ( ()) ⇒ 0 () = 0 ( ()) · 0 (), so 0 (1) = 0 ( (1)) · 0 (1) = 0 (3) · 4 = 9 · 4 = 36.

65. (a) () = (())

⇒ 0 () = 0 (()) 0 (). So 0 (1) = 0 ((1)) 0 (1) = 0 (3) 0 (1). To ﬁnd 0 (3), note that is

ot

1

3−4

= − . To ﬁnd 0 (1), note that is linear from (0 6) to (2 0), so its slope

6−2

4

1

0−6

= −3. Thus, 0 (3)0 (1) = − 4 (−3) = 3 . is 4

2−0

N

linear from (2 4) to (6 3), so its slope is

(b) () = ( ()) ⇒ 0 () = 0 ( ()) 0 (). So 0 (1) = 0 ( (1)) 0 (1) = 0 (2) 0 (1), which does not exist since

0 (2) does not exist.

(c) () = (()) ⇒ 0 () = 0 (()) 0 (). So 0 (1) = 0 ((1)) 0 (1) = 0 (3) 0 (1). To ﬁnd 0 (3), note that is linear from (2 0) to (5 2), so its slope is

2

2−0

= . Thus, 0 (3) 0 (1) = 2 (−3) = −2.

3

5−2

3

67. The point (3 2) is on the graph of , so (3) = 2. The tangent line at (3 2) has slope

() =

−4

2

∆

=

=− .

∆

6

3

() ⇒ 0 () = 1 [ ()]−12 · 0 () ⇒

2

√

1

0 (3) = 1 [ (3)]−12 · 0 (3) = 1 (2)−12 (− 2 ) = − √ or − 1 2.

2

2

3

6

3 2

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

78

¤

CHAPTER 2 DERIVATIVES

69. () = ((()))

⇒ 0 () = 0 ((())) · 0 (()) · 0 (), so

0 (1) = 0 (((1))) · 0 ((1)) · 0 (1) = 0 ((2)) · 0 (2) · 4 = 0 (3) · 5 · 4 = 6 · 5 · 4 = 120

71. () = (3 (4 ()))

⇒

0 () = 0 (3 (4 ())) ·

(3 (4 ())) = 0 (3 (4 ())) · 3 0 (4()) ·

(4())

= 0 (3 (4 ())) · 3 0 (4()) · 4 0 (), so

0 (0) = 0 (3 (4(0))) · 3 0 (4(0)) · 4 0 (0) = 0 (3 (4 · 0)) · 3 0 (4 · 0) · 4 · 2 = 0 (3 · 0) · 3 · 2 · 4 · 2 = 2 · 3 · 2 · 4 · 2 = 96.

73. Let () = cos . Then (2) = 2 0 (2), 2 (2) = 22 00 (2), 3 (2) = 23 000 (2), ,

() (2) = 2 () (2). Since the derivatives of cos occur in a cycle of four, and since 103 = 4(25) + 3, we have

77. (a) () = 40 + 035 sin

(b) At = 1,

2

54

⇒

=

7

2

=

cos

≈ 016.

54

54

79. By the Chain Rule, () =

1

4

cos(10)(10) =

5

2

cos(10) cms.

al

sin(10) ⇒ the velocity after seconds is () = 0 () =

2

2

07

2

7

2

035 cos

=

cos

=

cos

54

54

54

54

54

54

rS

1

4

=

=

() = () . The derivative is the rate of change of the velocity

Fo

75. () = 10 +

e

(103) () = (3) () = sin and 103 cos 2 = 2103 (103) (2) = 2103 sin 2.

with respect to time (in other words, the acceleration) whereas the derivative is the rate of change of the velocity with respect to the displacement.

( − 2)8

( − 2)9

− 18

, and the simpliﬁcation command results in the expression given by Derive.

9

(2 + 1)

(2 + 1)10

N

0 () = 9

45( − 2)8 without simplifying. With either Maple or Mathematica, we ﬁrst get

(2 + 1)10

ot

81. (a) Derive gives 0 () =

(b) Derive gives 0 = 2(3 − + 1)3 (2 + 1)4 (173 + 62 − 9 + 3) without simplifying. With either Maple or

Mathematica, we ﬁrst get 0 = 10(2 + 1)4 (3 − + 1)4 + 4(2 + 1)5 (3 − + 1)3 (32 − 1). If we use

Mathematica’s Factor or Simplify, or Maple’s factor, we get the above expression, but Maple’s simplify gives the polynomial expansion instead. For locating horizontal tangents, the factored form is the most helpful.

83. (a) If is even, then () = (−). Using the Chain Rule to differentiate this equation, we get

0 () = 0 (−)

(−) = − 0 (−). Thus, 0 (−) = − 0 (), so 0 is odd.

(b) If is odd, then () = − (−). Differentiating this equation, we get 0 () = − 0 (−)(−1) = 0 (−), so 0 is even. c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

SECTION 2.6 IMPLICIT DIFFERENTIATION

85. (a)

(sin cos ) = sin−1 cos cos + sin (− sin )

[Product Rule]

= sin−1 (cos cos − sin sin )

= sin−1 cos( + )

[Addition Formula for cosine]

= sin−1 cos[( + 1)]

(b)

[factor out sin−1 ]

[factor out ]

(cos cos ) = cos−1 (− sin ) cos + cos (− sin )

[Product Rule]

= − cos−1 (cos sin + sin cos )

= − cos−1 sin( + )

180

[factor out ]

rad, we have

(sin ◦ ) = sin 180 =

180

cos 180 =

180

cos ◦ .

e

[Addition Formula for sine]

= − cos−1 sin[( + 1)]

87. Since ◦ =

[factor out − cos−1 ]

=

, so

2

=

=

+

=

2

2

2

2

2

+

=

+

=

2

2

2

al

89. The Chain Rule says that

1. (a)

rS

Fo

2.6 Implicit Differentiation

9

(92 − 2 ) =

(1) ⇒ 18 − 2 0 = 0 ⇒ 2 0 = 18 ⇒ 0 =

⇒

ot

(b) 92 − 2 = 1 ⇒ 2 = 92 − 1

(b)

1

1

+

7.

=

1

1

+ =1 ⇒

(c) 0 = −

5.

√

9

= ± 92 − 1, so 0 = ± 1 (92 − 1)−12 (18) = ± √

.

2

92 − 1

9

9

= √

, which agrees with part (b).

± 92 − 1

N

(c) From part (a), 0 =

3. (a)

[Product Rule]

1

1

1

1

(1) ⇒ − 2 − 2 0 = 0 ⇒ − 2 0 = 2

1

1

−1

=1− =

⇒ =

⇒ 0 = −

2

2

( − 1)(1) − ()(1)

−1

, so 0 =

=

.

−1

( − 1)2

( − 1)2

2

[( − 1)] 2

2

1

=−

=− 2

=−

2

2

( − 1)2

( − 1)2

3

+ 3 =

(1) ⇒ 32 + 3 2 · 0 = 0 ⇒ 3 2 0 = −32

⇒ 0 = −

2

2

(2 + − 2 ) =

(4) ⇒ 2 + · 0 + · 1 − 2 0 = 0 ⇒

0 − 2 0 = −2 −

⇒ ( − 2) 0 = −2 −

⇒ 0 =

2 +

−2 −

=

− 2

2 −

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

¤

79

9.

¤

CHAPTER 2 DERIVATIVES

4

2

( + ) =

(3 − ) ⇒ 4 (1 + 0 ) + ( + ) · 43 = 2 (3 − 0 ) + (3 − ) · 2 0

4 + 4 0 + 44 + 43 = 3 2 − 2 0 + 6 0 − 2 2 0

(4 + 3 2 − 6) 0 = 3 2 − 54 − 43

⇒ cos · 0 − 2 0 = 2 + sin ⇒

2 + sin cos − 2

(4 cos sin ) =

(1) ⇒ 4 [cos · cos · 0 + sin · (− sin )] = 0 ⇒

0 (4 cos cos ) = 4 sin sin

15.

4 sin sin

= tan tan

4 cos cos

0 =

⇒

· 1 − · 0

= 1 + 0

[tan()] =

( + ) ⇒ sec2 () ·

2

⇒

sec2 () − sec2 () · 0 = 2 + 2 0

⇒ sec2 () − 2 = 2 0 + sec2 () ⇒

sec2 () − 2 = 2 + sec2 () · 0

⇒ 0 =

19.

0

− 2

2

1

()−12 ( 0

2

= 2 −

2

rS

⇒

+ · 1) = 0 + 2 0 + · 2 ⇒

Fo

= 1 + 2

sec2 () − 2

2 + sec2 ()

⇒

0

2

0 +

= 2 0 + 2

2

− 22

4 −

=

2

2

⇒ 0 =

( cos ) =

(1 + sin()) ⇒ (− sin ) + cos · 0 = cos() · (0 + · 1) ⇒

⇒

−

− 22

4

ot

17.

⇒

3 2 − 54 − 43

4 + 3 2 − 6

⇒ 0 =

2

( cos ) =

( + 2 ) ⇒ (− sin ) + cos · 0 = 2 + 2 0

0 (cos − 2) = 2 + sin ⇒ 0 =

13.

⇒ 4 0 + 3 2 0 − 6 0 = 3 2 − 54 − 43

al

11.

⇒

e

80

cos · 0 − cos() · 0 = sin + cos() ⇒ [cos − cos()] 0 = sin + cos() ⇒

21.

sin + cos() cos − cos()

N

0 =

() + 2 [ ()]3 =

(10) ⇒ 0 () + 2 · 3[ ()]2 · 0 () + [ ()]3 · 2 = 0. If = 1, we have

0 (1) + 12 · 3[ (1)]2 · 0 (1) + [ (1)]3 · 2(1) = 0 ⇒ 0 (1) + 1 · 3 · 22 · 0 (1) + 23 · 2 = 0 ⇒

0 (1) + 12 0 (1) = −16 ⇒ 13 0 (1) = −16 ⇒ 0 (1) = − 16 .

13

23.

4 2

( − 3 + 2 3 ) =

(0) ⇒ 4 · 2 + 2 · 43 0 − (3 · 1 + · 32 0 ) + 2( · 3 2 + 3 · 0 ) = 0 ⇒

43 2 0 − 32 0 + 2 3 0 = −24 + 3 − 6 2

0 =

⇒ (43 2 − 32 + 23 ) 0 = −24 + 3 − 6 2

−24 + 3 − 6 2

= 3 2

4 − 32 + 2 3

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

⇒

SECTION 2.6 IMPLICIT DIFFERENTIATION

25. sin 2 = cos 2

⇒

· cos 2 · 2 + sin 2 · 0 = (− sin 2 · 2 0 ) + cos(2) · 1

sin 2 · 0 + 2 sin 2 · 0 = −2 cos 2 + cos 2

0 (sin 2 + 2 sin 2) = −2 cos 2 + cos 2

0 =

0 =

81

⇒

⇒

−2 cos 2 + cos 2

. When = sin 2 + 2 sin 2

0 =

⇒

(−2)(−1) + 0

2

1

=

= , so an equation of the tangent line is −

0+·1

2

27. 2 + + 2 = 3

¤

4

2

and =

,

4

we have

= 1 ( − ), or = 1 .

2

2

2

⇒ 2 + 0 + · 1 + 20 = 0 ⇒ 0 + 2 0 = −2 −

⇒ 0 ( + 2) = −2 −

⇒

−3

−2 −

−2 − 1

. When = 1 and = 1, we have 0 =

=

= −1, so an equation of the tangent line is

+ 2

1+2·1

3

− 1 = −1( − 1) or = − + 2.

⇒ 2 + 2 0 = 2(22 + 2 2 − )(4 + 4 0 − 1). When = 0 and = 1 , we have

2

e

29. 2 + 2 = (22 + 2 2 − )2

0 + 0 = 2( 1 )(2 0 − 1) ⇒ 0 = 2 0 − 1 ⇒ 0 = 1, so an equation of the tangent line is −

2

4( + 0 )(2 + 2 ) = 25( − 0 )

⇒

rS

⇒ 4(2 + 2 )(2 + 2 0 ) = 25(2 − 2 0 ) ⇒

31. 2(2 + 2 )2 = 25(2 − 2 )

4 0 (2 + 2 ) + 250 = 25 − 4(2 + 2 ) ⇒

25 − 4(2 + 2 )

. When = 3 and = 1, we have 0 =

25 + 4(2 + 2 )

Fo

0 =

75 − 120

25 + 40

9

9

so an equation of the tangent line is − 1 = − 13 ( − 3) or = − 13 +

33. (a) 2 = 54 − 2

= 1( − 0)

al

or = + 1 .

2

1

2

⇒ 2 0 = 5(43 ) − 2 ⇒ 0 =

40

.

13

(b)

10(1)3 − 1

9

= , and an equation

2

2

ot

So at the point (1 2) we have 0 =

103 −

.

9

= − 45 = − 13 ,

65

N

of the tangent line is − 2 = 9 ( − 1) or = 9 − 5 .

2

2

2

⇒ 18 + 2 0 = 0 ⇒ 2 0 = −18 ⇒ 0 = −9 ⇒

− (−9)

2 + 92

· 1 − · 0

9

00 = −9

= −9

= −9 ·

= −9 · 3 [since x and y must satisfy the

2

2

3

35. 92 + 2 = 9

original equation, 92 + 2 = 9]. Thus, 00 = −81 3 .

37. 3 + 3 = 1

00 = −

⇒ 32 + 3 2 0 = 0 ⇒ 0 = −

2

2

⇒

2 (2) − 2 · 2 0

2 2 − 22 (−2 2 )

2 4 + 24

2( 3 + 3 )

2

=−

=−

=−

=− 5,

2 )2

4

6

(

6

since and must satisfy the original equation, 3 + 3 = 1.

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

82

¤

CHAPTER 2 DERIVATIVES

39. If = 0 in + 3 = 1, then we get 3 = 1

⇒ = 1, so the point where = 0 is (0 1). Differentiating implicitly with

respect to gives us 0 + · 1 + 32 0 = 0. Substituting 0 for and 1 for gives us 1 + 30 = 0 ⇒ 0 = − 1 .

3

Differentiating 0 + + 32 0 = 0 implicitly with respect to gives us 00 + 0 + 0 + 3(2 00 + 0 · 2 0 ) = 0. Now

substitute 0 for , 1 for , and − 1 for 0 . 0 − 1 − 1 + 3 00 + − 1 · 2 − 1 = 0 ⇒ 3 00 + 2 = 2 ⇒

3

3

3

3

3

9

3

00 +

2

9

=

2

9

⇒ 00 = 0.

41. (a) There are eight points with horizontal tangents: four at ≈ 157735 and

four at ≈ 042265.

(b) 0 =

32 − 6 + 2

2(2 3 − 3 2 − + 1)

⇒ 0 = −1 at (0 1) and 0 =

1

3

at (0 2).

(c) 0 = 0 ⇒ 32 − 6 + 2 = 0 ⇒ = 1 ±

1

3

√

3

al

(d) By multiplying the right side of the equation by − 3, we obtain the ﬁrst

e

Equations of the tangent lines are = − + 1 and = 1 + 2.

3

graph. By modifying the equation in other ways, we can generate the other

( 2 − 1)( − 2)

= ( − 1)( − 2)( − 3)

N

ot

Fo

rS

graphs.

( 2 − 4)( − 2)

= ( − 1)( − 2)

( + 1)(2 − 1)( − 2)

= ( − 1)( − 2)

( + 1)( 2 − 1)( − 2)

= ( − 1)( − 2)

( 2 + 1)( − 2)

= (2 − 1)( − 2)

( + 1)( 2 − 1)( − 2)

= ( − 1)( − 2)

( + 1)( 2 − 2)

= ( − 1)(2 − 2)

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

SECTION 2.6 IMPLICIT DIFFERENTIATION

43. From Exercise 31, a tangent to the lemniscate will be horizontal if 0 = 0

[25 − 4(2 + 2 )] = 0

⇒

45.

25

8

2

2

− 2 =1 ⇒

2

− 0 = we have

25

4

83

⇒ 25 − 4(2 + 2 ) = 0 ⇒

(1). (Note that when is 0, is also 0, and there is no horizontal tangent

for 2 + 2 in the equation of the lemniscate, 2(2 + 2 )2 = 25(2 − 2 ), we get

√

(2). Solving (1) and (2), we have 2 = 75 and 2 = 25 , so the four points are ± 5 4 3 ± 5 .

16

16

4

at the origin.) Substituting

2 − 2 =

2 + 2 =

¤

25

4

2

2 0

2

− 2 = 0 ⇒ 0 = 2

2

⇒ an equation of the tangent line at (0 0 ) is

2

2 0

0

0

0

0 2

0

( − 0 ). Multiplying both sides by 2 gives 2 − 2 = 2 − 2 . Since (0 0 ) lies on the hyperbola,

2

0

2

0

2

0

0

0

− 2 = 2 − 2 = 1.

2

0

−1

0

. The negative reciprocal of that slope is

=

, which is the slope of , so the tangent line at

0

−0 0

0

al

at (0 0 ) is −

⇒ 2 + 2 0 = 0 ⇒ 0 = − , so the slope of the tangent line

e

47. If the circle has radius , its equation is 2 + 2 = 2

is perpendicular to the radius .

and are not both zero]. 2 + 2 = 2

rS

49. 2 + 2 = 2 is a circle with center and + = 0 is a line through [assume

⇒ 2 + 2 0 = 0 ⇒ 0 = −, so the

slope of the tangent line at 0 (0 0 ) is −0 0 . The slope of the line 0 is 0 0 ,

Fo

which is the negative reciprocal of −0 0 . Hence, the curves are orthogonal, and the families of curves are orthogonal trajectories of each other.

⇒ 0 = 2 and 2 + 2 2 = [assume 0] ⇒ 2 + 4 0 = 0 ⇒

20 = −

1

=−

=−

, so the curves are orthogonal if

2()

2(2 )

2

ot

51. = 2

⇒ 0 = −

N

6= 0. If = 0, then the horizontal line = 2 = 0 intersects 2 + 2 2 = orthogonally

√ at ± 0 , since the ellipse 2 + 2 2 = has vertical tangents at those two points.

53. Since 2 2 , we are assured that there are four points of intersection.

(1)

2

2

+ 2 =1 ⇒

2

2

2 0

+ 2 =0 ⇒

2

0

=− 2

2

⇒ 0 = 1 = −

2

.

2

[continued]

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

84

¤

(2)

CHAPTER 2 DERIVATIVES

2

2

− 2 =1 ⇒

2

Now 1 2 = −

2

20

− 2 =0 ⇒

2

0

= 2

2

⇒ 0 = 2 =

2

.

2

2 2

2 2 2

2

2

2

2

·

= − 2 2 · 2 (3). Subtracting equations, (1) − (2), gives us 2 + 2 − 2 + 2 = 0 ⇒

2

2

2

2

2

2

+ 2 = 2 − 2

2

2 2 + 2 2

2 2 − 2 2

=

2 2

2 2

⇒

⇒

2 (2 + 2 )

2 (2 − 2 )

=

(4). Since

2 2

2 2

2 − 2 = 2 + 2 , we have 2 − 2 = 2 + 2 . Thus, equation (4) becomes

2

2

= 2 2

2 2

2

2 2

= 2 2 , and

2

⇒

2

2 2 2 2 in equation (3) gives us 1 2 = − 2 2 · 2 2 = −1. Hence, the ellipse and hyperbola are orthogonal

2

substituting for trajectories. ⇒ − +

2

3

=

−

2

⇒

al

( − + 2 −1 − 3 −2 ) =

( )

⇒

e

2

55. (a) + 2 ( − ) =

0 + · 1 − − 2 −2 · 0 + 23 −3 · 0 = 0 ⇒ 0 ( − 2 −2 + 23 −3 ) = −

−

3 ( − )

−

= or 3 −3

3 − 2 + 23

+ 2

rS

0 =

⇒

2 −2

(b) Using the last expression for from part (a), we get

−995733 L4

≈ −404 L atm

2464386541 L3 - atm

ot

=

Fo

(10 L)3 [(1 mole)(004267 Lmole) − 10 L]

=

(25 atm)(10 L)3 − (1 mole)2 (3592 L2 - atm mole2 )(10 L)

+ 2(1 mole)3 (3592 L2 - atm mole2 )(004267 L mole)

57. To ﬁnd the points at which the ellipse 2 − + 2 = 3 crosses the -axis, let = 0 and solve for .

N

√

√

= 0 ⇒ 2 − (0) + 02 = 3 ⇔ = ± 3. So the graph of the ellipse crosses the -axis at the points ± 3 0 .

Using implicit differentiation to ﬁnd 0 , we get 2 − 0 − + 20 = 0 ⇒ 0 (2 − ) = − 2 ⇔ 0 =

So 0 at

√

√

√

√

0−2 3

0+2 3

√ = 2 and 0 at − 3 0 is

√ = 2. Thus, the tangent lines at these points are parallel.

3 0 is

2(0) − 3

2(0) + 3

59. 2 2 + = 2

⇒ 2 · 2 0 + 2 · 2 + · 0 + · 1 = 0 ⇔ 0 (22 + ) = −22 −

2

0 = −

− 2

.

2 −

⇔

2

2 +

2 +

. So − 2

= −1 ⇔ 22 + = 22 + ⇔ (2 + 1) = (2 + 1) ⇔

22 +

2 +

(2 + 1) − (2 + 1) = 0 ⇔ (2 + 1)( − ) = 0 ⇔ = − 1 or = . But = − 1

2

2

2 2 + =

1

4

−

1

2

⇒

6= 2, so we must have = . Then 2 2 + = 2 ⇒ 4 + 2 = 2 ⇔ 4 + 2 − 2 = 0 ⇔

(2 + 2)(2 − 1) = 0. So 2 = −2, which is impossible, or 2 = 1 ⇔ = ±1. Since = , the points on the curve where the tangent line has a slope of −1 are (−1 −1) and (1 1). c ° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

SECTION 2.7

61. (a) = () and 00 + 0 + = 0

RATES OF CHANGE IN THE NATURAL AND SOCIAL SCIENCES

¤

85

⇒ 00 () + 0 () + () = 0. If = 0, we have 0 + 0 (0) + 0 = 0,

so 0 (0) = 0.

(b) Differentiating 00 + 0 + = 0 implicitly, we get 000 + 00 · 1 + 00 + 0 + · 1 = 0 ⇒

000 + 2 00 + 0 + = 0, so 000 () + 2 00 () + 0 () + () = 0. If = 0, we have

0 + 2 00 (0) + 0 + 1 [(0) = 1 is given] = 0 ⇒ 2 00 (0) = −1 ⇒ 00 (0) = − 1 .

2

2.7 Rates of Change in the Natural and Social Sciences

⇒ () = 0 () = 32 − 24 + 36 (in fts)

1. (a) = () = 3 − 122 + 36 (in feet)

e

(b) (3) = 27 − 72 + 36 = −9 fts

(c) The particle is at rest when () = 0. 32 − 24 + 36 = 0 ⇔ 3( − 2)( − 6) = 0 ⇔ = 2 s or 6 s.

al

(d) The particle is moving in the positive direction when () 0. 3( − 2)( − 6) 0 ⇔ 0 ≤ 2 or 6.

(e) Since the particle is moving in the positive direction and in the

(f)

rS

negative direction, we need to calculate the distance traveled in the intervals [0 2], [2 6], and [6 8] separately.

| (2) − (0)| = |32 − 0| = 32.

Fo

| (6) − (2)| = |0 − 32| = 32.

| (8) − (6)| = |32 − 0| = 32.

The total distance is 32 + 32 + 32 = 96 ft.

ot

(g) () = 32 − 24 + 36 ⇒

(h)

() = 0 () = 6 − 24.

N

(3) = 6(3) − 24 = −6 (fts)s or fts2 .

(i) The particle is speeding up when and have the same sign. This occurs when 2 4 [ and are both negative] and when 6 [ and are both positive]. It is slowing down when and have opposite signs; that is, when 0 ≤ 2 and when 4 6.

3. (a) = () = cos(4)

⇒ () = 0 () = − sin(4) · (4)

(b) (3) = − sin 3 = − ·

4

4

4

√

2

2

√

= − 8 2 fts [≈ −056]

(c) The particle is at rest when () = 0. − sin = 0 ⇒ sin = 0 ⇒

4

4

4

4

= ⇒ = 0, 4, 8 s.

(d) The particle is moving in the positive direction when () 0. − sin 0 ⇒ sin 0 ⇒ 4 8.

4

4

4

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

86

¤

CHAPTER 2

DERIVATIVES

(e) From part (c), () = 0 for = 0 4 8. As in Exercise 1, we’ll

(f)

ﬁnd the distance traveled in the intervals [0 4] and [4 8].

| (4) − (0)| = |−1 − 1| = 2

| (8) − (4)| = |1 − (−1)| = 2.

The total distance is 2 + 2 = 4 ft.

(g) () = −

sin

4

4

(h)

⇒

2

cos · = − cos .

4

4 4

16

4

√

√

2

2

2

2

3

2

(3) = − cos

=−

−

=

(fts)s or fts2 .

16

4

16

2

32

() = 0 () = −

e

(i) The particle is speeding up when and have the same sign. This occurs when 0 2 or 8 10 [ and are

al

both negative] and when 4 6 [ and are both positive]. It is slowing down when and have opposite signs; that is, when 2 4 and when 6 8.

rS

5. (a) From the ﬁgure, the velocity is positive on the interval (0 2) and negative on the interval (2 3). The acceleration is

positive (negative) when the slope of the tangent line is positive (negative), so the acceleration is positive on the interval

(0 1), and negative on the interval (1 3). The particle is speeding up when and have the same sign, that is, on the

Fo

interval (0 1) when 0 and 0, and on the interval (2 3) when 0 and 0. The particle is slowing down when and have opposite signs, that is, on the interval (1 2) when 0 and 0.

(b) 0 on (0 3) and 0 on (3 4). 0 on (1 2) and 0 on (0 1) and (2 4). The particle is speeding up on (1 2)

ot

[ 0, 0] and on (3 4) [ 0, 0]. The particle is slowing down on (0 1) and (2 3) [ 0, 0].

7. (a) () = 2 + 245 − 492

⇒ () = 0 () = 245 − 98. The velocity after 2 s is (2) = 245 − 98(2) = 49 ms

N

and after 4 s is (4) = 245 − 98(4) = −147 ms.

(b) The projectile reaches its maximum height when the velocity is zero. () = 0 ⇔ 245 − 98 = 0 ⇔

=

245

= 25 s.

98

(c) The maximum height occurs when = 25. (25) = 2 + 245(25) − 49(25)2 = 32625 m or 32 5 m .

8

(d) The projectile hits the ground when = 0 ⇔ 2 + 245 − 492 = 0 ⇔

−245 ± 2452 − 4(−49)(2)

=

⇒ = ≈ 508 s [since ≥ 0]

2(−49)

(e) The projectile hits the ground when = . Its velocity is ( ) = 245 − 98 ≈ −253 ms [downward].

9. (a) () = 15 − 1862

⇒

() = 0 () = 15 − 372. The velocity after 2 s is (2) = 15 − 372(2) = 756 ms.

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

SECTION 2.7

¤

RATES OF CHANGE IN THE NATURAL AND SOCIAL SCIENCES

15 ± 152 − 4(186)(25)

(b) 25 = ⇔ 1862 − 15 + 25 = 0 ⇔ =

2(186)

⇔ = 1 ≈ 235 or = 2 ≈ 571.

The velocities are (1 ) = 15 − 3721 ≈ 624 ms [upward] and (2 ) = 15 − 3722 ≈ −624 ms [downward].

⇒ 0 () = 2. 0 (15) = 30 mm2 mm is the rate at which

11. (a) () = 2

the area is increasing with respect to the side length as reaches 15 mm.

(b) The perimeter is () = 4, so 0 () = 2 = 1 (4) = 1 (). The

2

2

ﬁgure suggests that if ∆ is small, then the change in the area of the square is approximately half of its perimeter (2 of the 4 sides) times ∆. From the ﬁgure, ∆ = 2 (∆) + (∆)2 . If ∆ is small, then ∆ ≈ 2 (∆) and so ∆∆ ≈ 2.

(ii)

441 − 4

(21) − (2)

=

= 41

21 − 2

01

(b) () = 2

(25) − (2)

625 − 4

=

= 45

25 − 2

05

al

(iii)

(3) − (2)

9 − 4

=

= 5

3−2

1

rS

(i)

e

13. (a) Using () = 2 , we ﬁnd that the average rate of change is:

⇒ 0 () = 2, so 0 (2) = 4.

(c) The circumference is () = 2 = 0 (). The ﬁgure suggests that if ∆ is small, then the change in the area of the circle (a ring around the outside) is approximately

Fo

equal to its circumference times ∆. Straightening out this ring gives us a shape that is approximately rectangular with length 2 and width ∆, so ∆ ≈ 2(∆).

Algebraically, ∆ = ( + ∆) − () = ( + ∆)2 − 2 = 2(∆) + (∆)2 .

15. () = 42

0

ot

So we see that if ∆ is small, then ∆ ≈ 2(∆) and therefore, ∆∆ ≈ 2.

⇒ 0 () = 8

(a) (1) = 8 ft ft

⇒

(b) 0 (2) = 16 ft2 ft

(c) 0 (3) = 24 ft2 ft

N

2

As the radius increases, the surface area grows at an increasing rate. In fact, the rate of change is linear with respect to the radius. 17. The mass is () = 32 , so the linear density at is () = 0 () = 6.

(a) (1) = 6 kgm

(b) (2) = 12 kgm

(c) (3) = 18 kgm

Since is an increasing function, the density will be the highest at the right end of the rod and lowest at the left end.

19. The quantity of charge is () = 3 − 22 + 6 + 2, so the current is 0 () = 32 − 4 + 6.

(a) 0 (05) = 3(05)2 − 4(05) + 6 = 475 A

(b) 0 (1) = 3(1)2 − 4(1) + 6 = 5 A

The current is lowest when 0 has a minimum. 00 () = 6 − 4 0 when 2 . So the current decreases when

3

increases when 2 . Thus, the current is lowest at =

3

2

3

s.

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

2

3

and

87

88

¤

CHAPTER 2

DERIVATIVES

−12

2

21. With = 0 1 − 2

,

−12

−32

2

2

2

1

− 2

() = () +

() = 0 1 − 2

1− 2

()

· + · 0 −

=

2

−32

2

2

0

2

· 1− 2 + 2 =

= 0 1 − 2

(1 − 2 2 )32

Note that we factored out (1 − 2 2 )−32 since −32 was the lesser exponent. Also note that

() = .

23. (a) To ﬁnd the rate of change of volume with respect to pressure, we ﬁrst solve for in terms of .

=

⇒ =

⇒

= − 2.

110

210

1860 − 1750

2070 − 1860

=

= 11, 2 =

=

= 21,

1920 − 1910

10

1930 − 1920

10

rS

25. (a) 1920: 1 =

al

Thus, the volume is decreasing more rapidly at the beginning.

1

1

1

=−

− 2 =

=

=

(c) = −

( )

e

(b) From the formula for in part (a), we see that as increases, the absolute value of decreases.

(1 + 2 )/ 2 = (11 + 21)2 = 16 millionyear

740

830

4450 − 3710

5280 − 4450

=

= 74, 2 =

=

= 83,

1980 − 1970

10

1990 − 1980

10

Fo

1980: 1 =

(1 + 2 )/ 2 = (74 + 83)2 = 785 millionyear

(b) () = 3 + 2 + + (in millions of people), where ≈ 00012937063, ≈ −7061421911, ≈ 12,82297902,

ot

and ≈ −7,743,770396.

(c) () = 3 + 2 + + ⇒ 0 () = 32 + 2 + (in millions of people per year)

N

(d) 0 (1920) = 3(00012937063)(1920)2 + 2(−7061421911)(1920) + 12,82297902

≈ 14.48 millionyear [smaller than the answer in part (a), but close to it]

(1980) ≈ 75.29 millionyear (smaller, but close)

0

(e) 0 (1985) ≈ 81.62 millionyear, so the rate of growth in 1985 was about 8162 millionyear.

27. (a) Using =

() =

(b) () =

(2 − 2 ) with = 001, = 3, = 3000, and = 0027, we have as a function of :

4

3000

(0012 − 2 ). (0) = 0925 cms, (0005) = 0694 cms, (001) = 0.

4(0027)3

(2 − 2 ) ⇒ 0 () =

(−2) = −

. When = 3, = 3000, and = 0027, we have

4

4

2

0 () = −

3000

. 0 (0) = 0, 0 (0005) = −92592 (cms)cm, and 0 (001) = −185185 (cms)cm.

2(0027)3

(c) The velocity is greatest where = 0 (at the center) and the velocity is changing most where = = 001 cm

(at the edge). c ° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

SECTION 2.8

29. (a) () = 1200 + 12 − 012 + 000053

RELATED RATES

¤

89

⇒ 0 () = 12 − 02 + 000152 $yard, which is the marginal cost

function.

(b) 0 (200) = 12 − 02(200) + 00015(200)2 = $32yard, and this is the rate at which costs are increasing with respect to the production level when = 200. 0 (200) predicts the cost of producing the 201st yard

(c) The cost of manufacturing the 201st yard of fabric is (201) − (200) = 36322005 − 3600 ≈ $3220, which is approximately 0 (200).

31. (a) () =

()

⇒ 0 () =

0 () − () · 1

0 () − ()

=

.

2

2

0 () 0 ⇒ () is increasing; that is, the average productivity increases as the size of the workforce increases.

0 () − ()

0 ⇒ 0 () 0.

2

⇒ =

1

=

=

( ). Using the Product Rule, we have

(10)(00821)

0821

rS

33. =

⇒ 0 () () ⇒

al

0 () − () 0 ⇒

()

e

(b) 0 () is greater than the average productivity ⇒ 0 () () ⇒ 0 ()

1

1

=

[ () 0 () + () 0 ()] =

[(8)(−015) + (10)(010)] ≈ −02436 Kmin.

0821

0821

= 0 and

= 0.

Fo

35. (a) If the populations are stable, then the growth rates are neither positive nor negative; that is,

(b) “The caribou go extinct” means that the population is zero, or mathematically, = 0.

(c) We have the equations

= − and

= − + . Let = = 0, = 005, = 0001,

ot

= 005, and = 00001 to obtain 005 − 0001 = 0 (1) and −005 + 00001 = 0 (2). Adding 10 times

(2) to (1) eliminates the -terms and gives us 005 − 05 = 0 ⇒ = 10 . Substituting = 10 into (1)

N

results in 005(10 ) − 0001(10 ) = 0 ⇔ 05 − 001 2 = 0 ⇔ 50 − 2 = 0 ⇔

(50 − ) = 0 ⇔ = 0 or 50. Since = 10 , = 0 or 500. Thus, the population pairs ( ) that lead to stable populations are (0 0) and (500 50). So it is possible for the two species to live in harmony.

2.8 Related Rates

1. = 3

⇒

=

= 32

3. Let denote the side of a square. The square’s area is given by = 2 . Differentiating with respect to gives us

= 2 . When = 16, = 4. Substitution 4 for and 6 for gives us

= 2(4)(6) = 48 cm2s.

5. = 2 = (5)2 = 25

⇒

= 25

⇒ 3 = 25

⇒

3

= mmin.

25

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

90

¤

CHAPTER 2

7. (a) =

(b) =

DERIVATIVES

√

=3 ⇒

2 + 1 and

√

2 + 1

⇒

1

3

3

=

= (2 + 1)−12 · 2 · 3 = √

= √ = 1.

. When = 4,

2

2 + 1

9

2 = 2 + 1 ⇒ 2 = 2 − 1 ⇒ = 1 2 −

2

1

2

and

=5 ⇒

√

=

= · 5 = 5. When = 12, = 25 = 5, so

= 5(5) = 25.

9.

2

( + 2 + 2 ) =

(9) ⇒ 2

+ 2

+ 2

=0 ⇒

+

+

= 0. If

= 5,

= 4 and

( ) = (2 2 1), then 2(5) + 2(4) + 1

=0 ⇒

= −18.

11. (a) Given: a plane ﬂying horizontally at an altitude of 1 mi and a speed of 500 mih passes directly over a radar station.

If we let be time (in hours) and be the horizontal distance traveled by the plane (in mi), then we are given

e

that = 500 mih.

(c)

al

(b) Unknown: the rate at which the distance from the plane to the station is increasing

when it is 2 mi from the station. If we let be the distance from the plane to the station,

rS

then we want to ﬁnd when = 2 mi.

(d) By the Pythagorean Theorem, 2 = 2 + 1 ⇒ 2 () = 2 ().

√

√

√

3

=

= (500). Since 2 = 2 + 1, when = 2, = 3, so

=

(500) = 250 3 ≈ 433 mih.

2

Fo

(e)

13. (a) Given: a man 6 ft tall walks away from a street light mounted on a 15-ft-tall pole at a rate of 5 fts. If we let be time (in s)

and be the distance from the pole to the man (in ft), then we are given that = 5 fts.

(c)

ot

(b) Unknown: the rate at which the tip of his shadow is moving when he is 40 ft from the pole. If we let be the distance from the man to the tip of his

( + ) when = 40 ft.

N

shadow (in ft), then we want to ﬁnd

(d) By similar triangles,

+

15

=

6

⇒ 15 = 6 + 6

(e) The tip of the shadow moves at a rate of

15.

⇒ 9 = 6 ⇒ = 2 .

3

2

5

( + ) =

+ =

= 5 (5) =

3

3

3

We are given that

25

3

fts.

= 60 mih and

= 25 mih. 2 = 2 + 2

⇒

1

=

+

.

√

After 2 hours, = 2 (60) = 120 and = 2 (25) = 50 ⇒ = 1202 + 502 = 130,

1

120(60) + 50(25) so =

+

=

= 65 mih.

130

2

= 2

+ 2

⇒

=

+

⇒

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

SECTION 2.8

RELATED RATES

¤

91

= 4 fts and

= 5 fts. 2 = ( + )2 + 5002 ⇒

2

= 2( + )

+

. 15 minutes after the woman starts, we have

We are given that

17.

= (4 fts)(20 min)(60 smin) = 4800 ft and = 5 · 15 · 60 = 4500 ⇒

√

= (4800 + 4500)2 + 5002 = 86,740,000, so

837

+

4800 + 4500

(4 + 5) = √

≈ 899 fts

=

+

= √

86,740,000

8674

19. =

1

,

2

where is the base and is the altitude. We are given that

= 1 cmmin and

= 2 cm2 min. Using the

1

=

+

. When = 10 and = 100, we have 100 = 1 (10) ⇒

2

2

1

4 − 20

= 20, so 2 =

20 · 1 + 10

⇒ 4 = 20 + 10

⇒

=

= −16 cmmin.

2

10

1

2

= 10 ⇒

al

e

Product Rule, we have

= 35 kmh and

= 25 kmh. 2 = ( + )2 + 1002 ⇒

2

= 2( + )

+

. At 4:00 PM, = 4(35) = 140 and = 4(25) = 100 ⇒

√

= (140 + 100)2 + 1002 = 67,600 = 260, so

+

140 + 100

720

=

+

=

(35 + 25) =

≈ 554 kmh.

260

13

We are given that

Fo

rS

21.

23. If = the rate at which water is pumped in, then

= − 10,000, where

1 2

=

3

3

27

⇒

=

2

6

⇒ =

1

⇒

3

= 2

. When = 200 cm,

9

N

= 1

3

ot

= 1 2 is the volume at time . By similar triangles,

3

800,000

= 20 cmmin, so − 10,000 = (200)2 (20) ⇒ = 10,000 +

≈ 289,253 cm3min.

9

9

The ﬁgure is labeled in meters. The area of a trapezoid is

25.

1

(base1

2

+ base2 )(height), and the volume of the 10-meter-long trough is 10.

Thus, the volume of the trapezoid with height is = (10) 1 [03 + (03 + 2)].

2

By similar triangles,

Now

=

025

1

=

= , so 2 = ⇒ = 5(06 + ) = 3 + 52 .

05

2

⇒

02 = (3 + 10)

⇒

02

=

. When = 03,

3 + 10

02

02

1

10

=

= mmin = mmin or cmmin.

3 + 10(03)

6

30

3

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

92

¤

CHAPTER 2

DERIVATIVES

27. We are given that

2

1

1

3

=

= 30 ft3 min. = 2 =

3

3

2

12

2

4

=

⇒ 30 =

When = 10 ft,

⇒

120

6

= 2 =

≈ 038 ftmin.

10

5

29. =

1

,

2

but = 5 m and sin =

⇒

4

120

.

=

2

⇒ = 4 sin , so = 1 (5)(4 sin ) = 10 sin .

2

= 006 rads, so

=

= (10 cos )(006) = 06 cos .

= 06 cos

= (06) 1 = 03 m2s.

When = ,

2

3

3

We are given

= −015 m s, and

e

31. From the ﬁgure and given information, we have 2 + 2 = 2 ,

⇒ 2

+ 2

=0 ⇒

= − . Substituting the given

rS

2 + 2 = 2

al

= 02 m s when = 3 m. Differentiating implicitly with respect to , we get

information gives us (−015) = −3(02) ⇒ = 4 m. Thus, 32 + 42 = 2

2

Fo

= 25 ⇒ = 5 m.

⇒

33. Differentiating both sides of = with respect to and using the Product Rule gives us

+

=0 ⇒

600

=−

. When = 600, = 150 and

= 20, so we have

=−

(20) = −80. Thus, the volume is

150

ot

decreasing at a rate of 80 cm3min.

1

1

180

9

400

1

1

1

1

1

1

=

+

=

=

, so =

. Differentiating

=

+

=

+

1

2

80 100

8000

400

9

1

2

1

1 1

1 1

1 2

1 2

2

with respect to , we have − 2

=− 2

− 2

⇒

=

+ 2

. When 1 = 80 and

2

1

2

1

2

4002 1

1

107

= 2

≈ 0132 Ωs.

(03) +

(02) =

2 = 100,

9

802

1002

810

N

35. With 1 = 80 and 2 = 100,

37. We are given = 2◦min =

2

2

2

90

radmin. By the Law of Cosines,

= 12 + 15 − 2(12)(15) cos = 369 − 360 cos

2

= 360 sin

=

⇒

⇒

180 sin

=

. When = 60◦ ,

√

√

√

√

√

7

180 sin 60◦

3

√

=

= √ =

≈ 0396 mmin.

369 − 360 cos 60◦ = 189 = 3 21, so

21

3 21 90

3 21

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

SECTION 2.8

RELATED RATES

¤

93

39. (a) By the Pythagorean Theorem, 40002 + 2 = 2 . Differentiating with respect to ,

= 2 . We know that

= 600 fts, so when = 3000 ft,

√

√

= 40002 + 30002 = 25,000,000 = 5000 ft we obtain 2

and

3000

1800

=

=

(600) =

= 360 fts.

5000

5

(b) Here tan =

= 3000 ft,

4000

(tan ) =

4000

⇒

⇒

sec2

1

=

4000

⇒

cos2

=

. When

4000

4000

4000

4

(45)2

= 600 fts, = 5000 and cos =

=

= , so

=

(600) = 0096 rads.

5000

5

4000

1

2 1

−

⇒ − csc2

=

⇒ − csc

=

5

5

3

6

5

2

5 2

10

√

=

kmmin [≈ 130 mih]

=

6

9

3

41. cot =

al

e

⇒

= 300 kmh. By the Law of Cosines,

2 = 2 + 12 − 2(1)() cos 120◦ = 2 + 1 − 2 − 1 = 2 + + 1, so

2

= 2

+

=

⇒

2 + 1

=

. After 1 minute, =

2

Fo

2

rS

43. We are given that

√

√

52 + 5 + 1 = 31 km ⇒

300

60

= 5 km ⇒

2(5) + 1

1650

√

=

(300) = √

≈ 296 kmh.

2 31

31

45. Let the distance between the runner and the friend be . Then by the Law of Cosines,

ot

2 = 2002 + 1002 − 2 · 200 · 100 · cos = 50,000 − 40,000 cos (). Differentiating

N

implicitly with respect to , we obtain 2

= −40,000(− sin ) . Now if is the

distance run when the angle is radians, then by the formula for the length of an arc on a circle, = , we have = 100, so =

1

100

⇒

1

7

=

=

. To substitute into the expression for

100

100

, we must know sin at the time when = 200, which we ﬁnd from (): 2002 = 50,000 − 40,000 cos

√

√

2

15

15

7

cos = 1 ⇒ sin = 1 − 1 = 4 . Substituting, we get 2(200)

⇒

= 40,000 4 100

4

4

=

7

√

15

4

⇔

≈ 678 ms. Whether the distance between them is increasing or decreasing depends on the direction in which

the runner is running.

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

94

¤

CHAPTER 2 DERIVATIVES

2.9 Linear Approximations and Differentials

1. () = 4 + 32

⇒ 0 () = 43 + 6, so (−1) = 4 and 0 (−1) = −10.

Thus, () = (−1) + 0 (−1)( − (−1)) = 4 + (−10)( + 1) = −10 − 6.

√

√

⇒ 0 () = 1 −12 = 1(2 ), so (4) = 2 and 0 (4) = 1 . Thus,

2

4

3. () =

() = (4) + 0 (4)( − 4) = 2 + 1 ( − 4) = 2 + 1 − 1 = 1 + 1.

4

4

4

√

1 − ⇒ 0 () =

2

−1

√

, so (0) = 1 and 0 (0) = − 1 .

2

1−

al

Therefore,

√

1 − = () ≈ (0) + 0 (0)( − 0) = 1 + − 1 ( − 0) = 1 − 1 .

2

2

√

√

1

So 09 = 1 − 01 ≈ 1 − 2 (01) = 095

√

√ and 099 = 1 − 001 ≈ 1 − 1 (001) = 0995.

2

e

5. () =

√

4

1 + 2 ⇒ 0 () = 1 (1 + 2)−34 (2) = 1 (1 + 2)−34 , so

4

2

7. () =

rS

(0) = 1 and 0 (0) = 1 . Thus, () ≈ (0) + 0 (0)( − 0) = 1 + 1 .

2

2

√

√

We need 4 1 + 2 − 01 1 + 1 4 1 + 2 + 01, which is true when

2

1

= (1 + 2)−4

(1 + 2)4

9. () =

0 () = −4(1 + 2)−5 (2) =

⇒

Fo

−0368 0677.

−8

, so (0) = 1 and 0 (0) = −8.

(1 + 2)5

We need

ot

Thus, () ≈ (0) + 0 (0)( − 0) = 1 + (−8)( − 0) = 1 − 8.

1

1

− 01 1 − 8

+ 01, which is true

(1 + 2)4

(1 + 2)4

N

when − 0045 0055.

11. (a) The differential is deﬁned in terms of by the equation = 0 () . For = () = 2 sin 2,

0 () = 2 cos 2 · 2 + sin 2 · 2 = 2( cos 2 + sin 2), so = 2( cos 2 + sin 2) .

−12

1 + 2

(2) = √

1 + 2

√

√

√ 1 −12

√ 0 sec2 sec2

2

√ , so =

√ .

13. (a) For = () = tan , () = sec

·

=

2

2

2

(b) =

√

1 + 2

⇒ =

(b) For = () =

1

2

1 − 2

,

1 + 2

0 () =

(1 + 2 )(−2) − (1 − 2 )(2)

−2[(1 + 2 ) + (1 − 2 )]

−2(2)

−4

=

=

=

,

(1 + 2 )2

(1 + 2 )2

(1 + 2 )2

(1 + 2 )2

so =

−4

.

(1 + 2 )2

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

SECTION 2.9 LINEAR APPROXIMATIONS AND DIFFERENTIALS

15. (a) = tan

√

3 + 2

95

= sec2

⇒

(b) When = 4 and = −01, = [sec(4)]2 (−01) =

17. (a) =

¤

⇒ =

√ 2

2 (−01) = −02.

1

(3 + 2 )−12 (2) = √

2

3 + 2

1

1

(b) = 1 and = −01 ⇒ = √

(−01) = (−01) = −005.

2

3 + 12

19. = () = 2 − 2 , = 2, ∆ = −04

⇒

∆ = (16) − (2) = 064 − 0 = 064

= −

2

5

−

2

4

= −01

2

2

= − 2 (1) = −0125

2

4

rS

∆ = (5) − (4) =

⇒

al

21. = () = 2, = 4, ∆ = 1

e

= (2 − 2) = (2 − 4)(−04) = 08

Fo

23. To estimate (1999)4 , we’ll ﬁnd the linearization of () = 4 at = 2. Since 0 () = 43 , (2) = 16, and

0 (2) = 32, we have () = 16 + 32( − 2). Thus, 4 ≈ 16 + 32( − 2) when is near 2, so

(1999)4 ≈ 16 + 32(1999 − 2) = 16 − 0032 = 15968.

25. = () =

√

3

⇒ = 1 −23 . When = 1000 and = 1, = 1 (1000)−23 (1) =

3

3

ot

√

3

1001 = (1001) ≈ (1000) + = 10 +

1

300

1

300 ,

so

= 10003 ≈ 10003.

⇒ = sec2 . When = 45◦ and = −1◦ ,

√ 2

= sec2 45◦ (−180) =

2 (−180) = −90, so tan 44◦ = (44◦ ) ≈ (45◦ ) + = 1 − 90 ≈ 0965.

N

27. = () = tan

29. = () = sec

⇒ 0 () = sec tan , so (0) = 1 and 0 (0) = 1 · 0 = 0. The linear approximation of at 0 is

(0) + 0 (0)( − 0) = 1 + 0() = 1. Since 008 is close to 0, approximating sec 008 with 1 is reasonable.

31. (a) If is the edge length, then = 3

⇒ = 32 . When = 30 and = 01, = 3(30)2 (01) = 270, so the

maximum possible error in computing the volume of the cube is about 270 cm3 . The relative error is calculated by dividing the change in , ∆ , by . We approximate ∆ with .

∆

32

01

Relative error =

≈

=

=3

= 001.

=3

3

30

Percentage error = relative error × 100% = 001 × 100% = 1%.

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

96

¤

CHAPTER 2 DERIVATIVES

(b) = 62

⇒ = 12 . When = 30 and = 01, = 12(30)(01) = 36, so the maximum possible error in

computing the surface area of the cube is about 36 cm2 .

12

01

∆

≈

=

=2

= 0006.

=2

Relative error =

62

30

Percentage error = relative error × 100% = 0006 × 100% = 06%.

33. (a) For a sphere of radius , the circumference is = 2 and the surface area is = 42 , so

2

2

2

⇒ = 4

=

2

so the maximum error is about

⇒ =

1 2

. When = 84 and = 05,

22

e

=

2

2

84

. When = 84 and = 05, = (84)(05) =

,

84

84

1

≈ 27 cm2 . Relative error ≈

= 2

=

≈ 0012 = 12%

84

84

3

4 3

4

3

=

=

3

3

2

62

(b) =

⇒ =

1

1764

1764

(84)2 (05) =

, so the maximum error is about 2 ≈ 179 cm3 .

22

2

35. (a) = 2

17642

1

=

=

≈ 0018 = 18%.

(84)3(62 )

56

rS

The relative error is approximately

al

=

⇒ ∆ ≈ = 2 = 2 ∆

(b) The error is

37. =

⇒ =

⇒ = −

Fo

∆ − = [( + ∆)2 − 2 ] − 2 ∆ = 2 + 2 ∆ + (∆)2 − 2 − 2 ∆ = (∆)2 .

∆

−( 2 )

. The relative error in calculating is

≈

=

=−

.

2

Hence, the relative error in calculating is approximately the same (in magnitude) as the relative error in .

= 0 = 0

(b) () =

ot

39. (a) =

+

=

+

= +

N

( + ) =

(c) ( + ) =

() =

=

(d) () =

() =

+

=

+

= +

−

−

−

=

=

=

=

(e)

2

2

2

(f ) ( ) =

( ) = −1

41. (a) The graph shows that 0 (1) = 2, so () = (1) + 0 (1)( − 1) = 5 + 2( − 1) = 2 + 3.

(09) ≈ (09) = 48 and (11) ≈ (11) = 52.

(b) From the graph, we see that 0 () is positive and decreasing. This means that the slopes of the tangent lines are positive, but the tangents are becoming less steep. So the tangent lines lie above the curve. Thus, the estimates in part (a) are too large. c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

CHAPTER 2 REVIEW

¤

97

2 Review

1. See Deﬁnition 2.1.1.

2. See the paragraph containing Formula 3 in Section 2.1.

3. (a) The average rate of change of with respect to over the interval [1 2 ] is

(b) The instantaneous rate of change of with respect to at = 1 is lim

2 →1

(2 ) − (1 )

.

2 − 1

(2 ) − (1 )

.

2 − 1

4. See Deﬁnition 2.1.4. The pages following the deﬁnition discuss interpretations of 0 () as the slope of a tangent line to the

graph of at = and as an instantaneous rate of change of () with respect to when = .

(b)

e

5. (a) A function is differentiable at a number if its derivative 0 exists

at = ; that is, if () exists.

al

0

(c) See Theorem 2.2.4. This theorem also tells us that if is not

rS

continuous at , then is not differentiable at .

6. See the discussion and Figure 7 on page 120.

7. The second derivative of a function is the rate of change of the ﬁrst derivative 0 . The third derivative is the derivative (rate

Fo

of change) of the second derivative. If is the position function of an object, 0 is its velocity function, 00 is its acceleration function, and 000 is its jerk function.

8. (a) The Power Rule: If is any real number, then

( ) = −1 . The derivative of a variable base raised to a constant

ot

power is the power times the base raised to the power minus one.

(b) The Constant Multiple Rule: If is a constant and is a differentiable function, then

[ ()] =

().

N

The derivative of a constant times a function is the constant times the derivative of the function.

(c) The Sum Rule: If and are both differentiable, then

[ () + ()] =

() +

(). The derivative of a sum

of functions is the sum of the derivatives.

(d) The Difference Rule: If and are both differentiable, then

[ () − ()] =

() −

(). The derivative of a

difference of functions is the difference of the derivatives.

(e) The Product Rule: If and are both differentiable, then

[ () ()] = ()

() + ()

(). The

derivative of a product of two functions is the ﬁrst function times the derivative of the second function plus the second function times the derivative of the ﬁrst function.

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

98

¤

CHAPTER 2 DERIVATIVES

() () − () ()

()

=

(f ) The Quotient Rule: If and are both differentiable, then

.

()

[ ()]2

The derivative of a quotient of functions is the denominator times the derivative of the numerator minus the numerator times the derivative of the denominator, all divided by the square of the denominator.

(g) The Chain Rule: If and are both differentiable and = ◦ is the composite function deﬁned by () = (()), then is differentiable and 0 is given by the product 0 () = 0 (()) 0 (). The derivative of a composite function is the derivative of the outer function evaluated at the inner function times the derivative of the inner function.

9. (a) =

⇒ 0 = −1

(b) = sin ⇒ 0 = cos

(c) = cos ⇒ 0 = − sin

(d) = tan ⇒ 0 = sec2

(e) = csc ⇒ 0 = − csc cot

(f) = sec ⇒ 0 = sec tan

e

(g) = cot ⇒ 0 = − csc2

10. Implicit differentiation consists of differentiating both sides of an equation involving and with respect to , and then

al

solving the resulting equation for 0 .

rS

11. See the examples in Section 2.7 as well as the text following Example 8.

12. (a) The linearization of at = is () = () + 0 ()( − ).

(b) If = (), then the differential is given by = 0 () .

Fo

(c) See Figure 5 in Section 2.9.

See the note after Theorem 4 in Section 2.2.

3. False.

See the warning before the Product Rule.

7. False.

0 ()

1

() =

[ ()]12 = [ ()]−12 0 () =

2

2 ()

N

5. True.

ot

1. False.

() = 2 + = 2 + for ≥ 0 or ≤ −1 and 2 + = −(2 + ) for −1 0.

So 0 () = 2 + 1 for 0 or −1 and 0 () = −(2 + 1) for −1 0. But |2 + 1| = 2 + 1 for ≥ − 1 and |2 + 1| = −2 − 1 for − 1 .

2

2

9. True.

() = 5 lim →2

11. False.

⇒ 0 () = 54

⇒ 0 (2) = 5(2)4 = 80, and by the deﬁnition of the derivative,

() − (2)

= 0 (2) = 80.

−2

A tangent line to the parabola = 2 has slope = 2, so at (−2 4) the slope of the tangent is 2(−2) = −4 and an equation of the tangent line is − 4 = −4( + 2). [The given equation, − 4 = 2( + 2), is not even

linear!]

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

CHAPTER 2 REVIEW

¤

1. (a) = () = 1 + 2 + 2 4. The average velocity over the time interval [1 1 + ] is

ave =

1 + 2(1 + ) + (1 + )2 4 − 134

10 + 2

10 +

(1 + ) − (1)

=

=

=

(1 + ) − 1

4

4

So for the following intervals the average velocities are:

(i) [1 3]: = 2, ave = (10 + 2)4 = 3 ms

(ii) [1 2]: = 1, ave = (10 + 1)4 = 275 ms

(iii) [1 15]: = 05, ave = (10 + 05)4 = 2625 ms

(b) When = 1, the instantaneous velocity is lim

→0

(iv) [1 11]: = 01, ave = (10 + 01)4 = 2525 ms

(1 + ) − (1)

10 +

10

= lim

=

= 25 ms.

→0

4

4

5. The graph of has tangent lines with positive slope for 0 and negative

e

3.

al

slope for 0, and the values of ﬁt this pattern, so must be the graph of the derivative of the function for . The graph of has horizontal tangent

rS

lines to the left and right of the -axis and has zeros at these points. Hence,

is the graph of the derivative of the function for . Therefore, is the graph

ot

Fo

of , is the graph of 0 , and is the graph of 00 .

7. (a) 0 () is the rate at which the total cost changes with respect to the interest rate. Its units are dollars(percent per year).

N

(b) The total cost of paying off the loan is increasing by $1200(percent per year) as the interest rate reaches 10%. So if the interest rate goes up from 10% to 11%, the cost goes up approximately $1200.

(c) As increases, increases. So 0 () will always be positive.

9. 0 (1990) is the rate at which the total value of US currency in circulation is changing in billions of dollars per year. To

estimate the value of 0 (1990), we will average the difference quotients obtained using the times = 1985 and = 1995.

Let =

=

1873 − 2719

−846

(1985) − (1990)

=

=

= 1692 and

1985 − 1990

−5

−5

(1995) − (1990)

4093 − 2719

1374

=

=

= 2748. Then

1995 − 1990

5

5

0 (1990) = lim

→1990

() − (1990)

+

1692 + 2748

444

≈

=

=

= 222 billion dollarsyear.

− 1990

2

2

2

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

99

¤

CHAPTER 2 DERIVATIVES

11. () = 3 + 5 + 4

0 () = lim

→0

= lim

→0

( + ) − ()

( + )3 + 5( + ) + 4 − (3 + 5 + 4)

= lim

→0

32 + 32 + 3 + 5

= lim (32 + 3 + 2 + 5) = 32 + 5

→0

⇒ 0 = 4(2 + 3 )3 (2 + 32 ) = 4(2 )3 (1 + )3 (2 + 3) = 47 ( + 1)3 (3 + 2)

13. = (2 + 3 )4

2 − + 2

√

= 32 − 12 + 2−12

4 − 1

4 + 1

⇒ 0 =

(4 + 1)43 − (4 − 1)43

43 [(4 + 1) − (4 − 1)]

83

=

= 4

4 + 1)2

4 + 1)2

(

(

( + 1)2

√

√

sec2 1 −

1

√

(−1) = − √

⇒ 0 = sec2 1 −

2 1−

2 1−

√

al

21. = tan 1 −

23.

3 12 1 −12

3√

1

1

−

− −32 =

− √ − √

2

2

2

2

3

⇒ 0 = 2 (cos ) + (sin )(2) = ( cos + 2 sin )

17. = 2 sin

19. =

⇒ 0 =

e

15. =

⇒

( 4 + 2 ) =

( + 3) ⇒ · 4 3 0 + 4 · 1 + 2 · 0 + · 2 = 1 + 3 0

0 (4 3 + 2 − 3) = 1 − 4 − 2 sec 2

1 + tan 2

⇒

⇒

1 − 4 − 2

4 3 + 2 − 3

Fo

25. =

⇒ 0 =

rS

100

(1 + tan 2)(sec 2 tan 2 · 2) − (sec 2)(sec2 2 · 2)

2 sec 2 [(1 + tan 2) tan 2 − sec2 2]

=

(1 + tan 2)2

(1 + tan 2)2

2

2

2 sec 2 (tan 2 + tan 2 − sec 2)

2 sec 2 (tan 2 − 1)

1 + tan2 = sec2

=

=

(1 + tan 2)2

(1 + tan 2)2

27. = (1 − −1 )−1

⇒

ot

0 =

N

0 = −1(1 − −1 )−2 [−(−1−2 )] = −(1 − 1)−2 −2 = −(( − 1))−2 −2 = −( − 1)−2

29. sin() = 2 −

⇒ cos()(0 + · 1) = 2 − 0

0 [ cos() + 1] = 2 − cos() ⇒ 0 =

31. = cot(32 + 5)

⇒ cos() 0 + 0 = 2 − cos() ⇒

2 − cos()

cos() + 1

⇒ 0 = − csc2 (32 + 5)(6) = −6 csc2 (32 + 5)

√

√

cos ⇒

√

√

√ 0

√ √ 0 √

√

0 = cos + cos

= − sin 1 −12 + cos 1 −12

2

2

33. =

=

1 −12

2

√

√

√

√

√

√ cos − sin

√

− sin + cos =

2

2

35. = tan2 (sin ) = [tan(sin )]

⇒ 0 = 2[tan(sin )] · sec2 (sin ) · cos

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

CHAPTER 2 REVIEW

37. = ( tan )15

39. = sin tan

41. () =

¤

⇒ 0 = 1 ( tan )−45 (tan + sec2 )

5

√

√

√

√

⇒ 0 = cos tan 1 + 3 sec2 1 + 3 32 2 1 + 3

1 + 3

√

4 + 1 ⇒ 0 () =

1

2 (4

+ 1)−12 · 4 = 2(4 + 1)−12

⇒

4

00 () = 2(− 1 )(4 + 1)−32 · 4 = −4(4 + 1)32 , so 00 (2) = −4932 = − 27 .

2

⇒ 65 + 6 5 0 = 0 ⇒ 0 = −5 5

43. 6 + 6 = 1

⇒

54 4 − (−5 5 )

54 ( 6 + 6 ) 5

5 (54 ) − 5 (5 4 0 )

54

00

=−

=−

=−

= − 11

( 5 )2

10

6

→0

sec sec 0

1

=

=

=1

1 − sin

1 − sin 0

1−0

⇒ 0 = 4 · 2 sin cos . At 1 , 0 = 8 ·

6

√

√

√

is − 1 = 2 3 − , or = 2 3 + 1 − 33.

6

·

√

3

2

=2

√

3, so an equation of the tangent line

√

2 cos

1 + 4 sin ⇒ 0 = 1 (1 + 4 sin )−12 · 4 cos = √

.

2

1 + 4 sin

rS

49. =

1

2

al

47. = 4 sin2

e

45. lim

2

At (0 1), 0 = √ = 2, so an equation of the tangent line is − 1 = 2( − 0), or = 2 + 1.

1

The slope of the normal line is − 1 , so an equation of the normal line is − 1 = − 1 ( − 0), or = − 1 + 1.

2

2

2

Fo

√

5− ⇒

√

√

√

−

2(5 − )

1

−

2 5−

0 () = (5 − )−12 (−1) + 5 − = √

+ 5−· √

= √

+ √

2

2 5−

2 5−

2 5−

2 5−

51. (a) () =

10 − 3

− + 10 − 2

√

= √

2 5−

2 5−

ot

=

(b) At (1 2): 0 (1) = 7 .

4

(c)

N

So an equation of the tangent line is − 2 = 7 ( − 1) or = 7 + 1 .

4

4

4

At (4 4): 0 (4) = − 2 = −1.

2

So an equation of the tangent line is − 4 = −1( − 4) or = − + 8.

The graphs look reasonable, since 0 is positive where has tangents with

(d)

positive slope, and 0 is negative where has tangents with negative slope.

⇒ 0 = cos − sin = 0 ⇔ cos = sin and 0 ≤ ≤ 2

√

√ are 2 and 5 − 2 .

4

4

53. = sin + cos

⇔ =

4

or

5

,

4

so the points

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

101

102

¤

CHAPTER 2 DERIVATIVES

55. = () = 2 + +

⇒ 0 () = 2 + . We know that 0 (−1) = 6 and 0 (5) = −2, so −2 + = 6 and

10 + = −2. Subtracting the ﬁrst equation from the second gives 12 = −8 ⇒ = − 2 . Substituting − 2 for in the

3

3 ﬁrst equation gives =

14

.

3

Now (1) = 4 ⇒ 4 = + + , so = 4 +

57. () = ( − )( − )( − )

So

2

3

−

14

3

= 0 and hence, () = − 2 2 +

3

14

.

3

⇒ 0 () = ( − )( − ) + ( − )( − ) + ( − )( − ).

0 ()

( − )( − ) + ( − )( − ) + ( − )( − )

1

1

1

=

=

+

+

.

()

( − )( − )( − )

−

−

−

⇒ 0 () = () 0 () + () 0 () ⇒

59. (a) () = () ()

0 (2) = (2) 0 (2) + (2) 0 (2) = (3)(4) + (5)(−2) = 12 − 10 = 2

(b) () = (()) ⇒ 0 () = 0 (()) 0 () ⇒ 0 (2) = 0 ((2)) 0 (2) = 0 (5)(4) = 11 · 4 = 44

⇒ 0 () = 2 0 () + ()(2) = [0 () + 2()]

63. () = [ ()]2

⇒ 0 () = 2[ ()] · 0 () = 2() 0 ()

65. () = (())

⇒ 0 () = 0 (()) 0 ()

67. () = (sin )

⇒ 0 () = 0 (sin ) · cos

⇒

al rS 0 () =

() ()

() + ()

[ () + ()] [ () 0 () + () 0 ()] − () () [ 0 () + 0 ()]

[ () + ()]2

Fo

69. () =

e

61. () = 2 ()

[ ()]2 0 () + () () 0 () + () () 0 () + [ ()]2 0 () − () () 0 () − () () 0 ()

[() + ()]2

=

0 () [ ()]2 + 0 () [ ()]2

[ () + ()]2

ot

=

71. Using the Chain Rule repeatedly, () = ((sin 4))

⇒

((sin 4)) = 0 ((sin 4)) · 0 (sin 4) ·

(sin 4) = 0 ((sin 4)) 0 (sin 4)(cos 4)(4).

N

0 () = 0 ((sin 4)) ·

73. (a) = 3 − 12 + 3

⇒ () = 0 = 32 − 12 ⇒ () = 0 () = 6

(b) () = 3(2 − 4) 0 when 2, so it moves upward when 2 and downward when 0 ≤ 2.

(c) Distance upward = (3) − (2) = −6 − (−13) = 7,

Distance downward = (0) − (2) = 3 − (−13) = 16. Total distance = 7 + 16 = 23.

(d)

(e) The particle is speeding up when and have the same sign, that is, when 2. The particle is slowing down when and have opposite signs; that is, when 0 2.

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

CHAPTER 2 REVIEW

¤

75. The linear density is the rate of change of mass with respect to length .

√

= 1 + = + 32

77. If = edge length, then = 3

⇒ = = 1 +

3

2

√

√

, so the linear density when = 4 is 1 + 3 4 = 4 kgm.

2

⇒ = 32 = 10 ⇒ = 10(32 ) and = 62

= (12) = 12[10(32 )] = 40. When = 30, =

79. Given = 5 and = 15, ﬁnd . 2 = 2 + 2

2

= 2

+ 2

40

30

=

4

3

⇒

cm2 min.

⇒

1

⇒

= (15 + 5). When = 3,

√

= 45 + 3(5) = 60 and = 15(3) = 45 ⇒ = 452 + 602 = 75,

1

=

[15(45) + 5(60)] = 13 fts.

75

= 400 cot

⇒

⇒

= −400 csc2 . When =

,

6

rS

= −400(2)2 (−025) = 400 fth.

√

3

1 + 3 = (1 + 3)13

e

81. We are given = −025 radh. tan = 400

al

so

⇒ 0 () = (1 + 3)−23 , so the linearization of at = 0 is

√

() = (0) + 0 (0)( − 0) = 113 + 1−23 = 1 + . Thus, 3 1 + 3 ≈ 1 + ⇒

√

3

103 = 3 1 + 3(001) ≈ 1 + (001) = 101.

Fo

83. (a) () =

√

(b) The linear approximation is 3 1 + 3 ≈ 1 + , so for the required accuracy

√

√ we want 3 1 + 3 − 01 1 + 3 1 + 3 + 01. From the graph,

ot

it appears that this is true when −0235 0401.

N

1 2

= 1 + 2 ⇒ = 2 + . When = 60

2

8

4

and = 01, = 2 + 60(01) = 12 + 3 , so the maximum error is

4

2

85. = 2 + 1

2

approximately 12 +

87. lim

→0

3

2

≈ 167 cm2 .

√

4

16 + − 2

√

1

1

1

4

=

= −34

= √ 3 =

4

32

4 4 16

= 16

= 16

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

103

104

¤

CHAPTER 2 DERIVATIVES

√

√

√

√

√

√

1 + tan − 1 + sin

1 + tan + 1 + sin

1 + tan − 1 + sin

√

√

89. lim

= lim

→0

→0

3

3

1 + tan + 1 + sin

= lim

→0

= lim

→0

3

3

cos

(1 + tan ) − (1 + sin ) sin (1 cos − 1)

= lim √

·

√

√

√

→0 3 cos

1 + tan + 1 + sin

1 + tan + 1 + sin

1 + cos sin (1 − cos )

√

√

·

1 + tan + 1 + sin cos 1 + cos

sin · sin2

√

√

→0 3

1 + tan + 1 + sin cos (1 + cos )

3

sin

1

√

lim √

= lim

→0

→0

1 + tan + 1 + sin cos (1 + cos )

= lim

1 2

= 1 2 , so 0 () = 1 2 .

2

8

8

e

⇒ 0 (2) · 2 = 2

⇒ 0 (2) = 1 2 . Let = 2. Then 0 () =

2

1

2

ot

Fo

rS

al

[ (2)] = 2

N

91.

1

1

√

= 13 · √

=

4

1 + 1 · 1 · (1 + 1)

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

PROBLEMS PLUS

1. Let be the -coordinate of . Since the derivative of = 1 − 2 is 0 = −2, the slope at is −2. But since the triangle

√

√

√

√

31, so the slope at is − 3. Therefore, we must have that −2 = − 3 ⇒ = 23 .

√

√

√ 2 √

3

= 23 1 and by symmetry, has coordinates − 23 1 .

Thus, the point has coordinates 2 1 − 23

4

4

is equilateral, =

We must show that (in the ﬁgure) is halfway between and , that is,

3.

= ( + )2. For the parabola = 2 + + , the slope of the tangent line is given by 0 = 2 + . An equation of the tangent line at = is

− (2 + + ) = (2 + )( − ). Solving for gives us

e

= (2 + ) − 22 − + (2 + + ) or (1)

al

= (2 + ) + − 2

Similarly, an equation of the tangent line at = is

rS

= (2 + ) + − 2

(2)

We can eliminate and solve for by subtracting equation (1) from equation (2).

[(2 + ) − (2 + )] − 2 + 2 = 0

Fo

(2 − 2) = 2 − 2

2( − ) = ( 2 − 2 )

=

+

( + )( − )

=

2( − )

2

ot

Thus, the -coordinate of the point of intersection of the two tangent lines, namely , is ( + )2.

5. Using 0 () = lim

→

() − () sec − sec

, we recognize the given expression, () = lim

, as

→

−

−

N

0 () with () = sec . Now 0 ( ) = 00 ( ), so we will ﬁnd 00 ().

4

4

0 () = sec tan ⇒ 00 () = sec sec2 + tan sec tan = sec (sec2 + tan2 ), so

√ √ 2

√

√

00 ( ) = 2( 2 + 12 ) = 2(2 + 1) = 3 2.

4

7. We use mathematical induction. Let be the statement that

(sin4 + cos4 ) = 4−1 cos(4 + 2).

1 is true because

(sin4 + cos4 ) = 4 sin3 cos − 4 cos3 sin = 4 sin cos sin2 − cos2

= −4 sin cos cos 2 = −2 sin 2 cos 2 = − sin 4 = sin(−4)

= cos − (−4) = cos + 4 = 4−1 cos 4 + when = 1

2

2

2

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

[continued]

105

106

¤

CHAPTER 2 PROBLEMS PLUS

4 sin + cos4 = 4−1 cos 4 + . Then

2

−1

(sin4 + cos4 ) =

(sin4 + cos4 ) = cos 4 +

4

2

Now assume is true, that is,

+1

+1

which shows that +1 is true.

Therefore,

4 + = −4 sin 4 +

= −4−1 sin 4 + ·

2

2

2

= 4 sin −4 − 2 = 4 cos − −4 − = 4 cos 4 + ( + 1)

2

2

2

(sin4 + cos4 ) = 4−1 cos 4 + for every positive integer , by mathematical induction.

2

Another proof: First write

sin4 + cos4 = (sin2 + cos2 )2 − 2 sin2 cos2 = 1 −

(sin4 + cos4 ) =

sin2 2 = 1 − 1 (1 − cos 4) =

4

3

4

+

1

4

cos 4

3

1

1

+ cos 4 = · 4 cos 4 +

= 4−1 cos 4 + .

4

4

4

2

2

e

Then we have

1

2

1 and pass through ±0 2 respectively, so the

0

±20

rS

points ±0 2 . The normals to = 2 at = ±0 have slopes −

0

al

9. We must ﬁnd a value 0 such that the normal lines to the parabola = 2 at = ±0 intersect at a point one unit from the

1

1

1

( − 0 ) and − 2 =

( + 0 ). The common -intercept is 2 + .

0

0

20

20

2

We want to ﬁnd the value of 0 for which the distance from 0 2 + 1 to 0 2 equals 1. The square of the distance is

0

0

2

normals have the equations − 2 = −

0

√

Fo

2

= 2 +

(0 − 0)2 + 2 − 2 + 1

0

0

0

2

5 the center of the circle is at 0 4 .

1

4

= 1 ⇔ 0 = ±

3

.

2

For these values of 0 , the -intercept is 2 +

0

1

2

= 5 , so

4

ot

Another solution: Let the center of the circle be (0 ). Then the equation of the circle is 2 + ( − )2 = 1.

Solving with the equation of the parabola, = 2 , we get 2 + (2 − )2 = 1 ⇔ 2 + 4 − 22 + 2 = 1 ⇔

N

4 + (1 − 2)2 + 2 − 1 = 0. The parabola and the circle will be tangent to each other when this quadratic equation in 2 has equal roots; that is, when the discriminant is 0. Thus, (1 − 2)2 − 4(2 − 1) = 0 ⇔

1 − 4 + 42 − 42 + 4 = 0 ⇔ 4 = 5, so = 5 . The center of the circle is 0 5 .

4

4

11. We can assume without loss of generality that = 0 at time = 0, so that = 12 rad. [The angular velocity of the wheel

is 360 rpm = 360 · (2 rad)(60 s) = 12 rads.] Then the position of as a function of time is

40 sin sin

1

=

=

= sin 12.

12 m

120

3

3

1

= · 12 · cos 12 = 4 cos . When = , we have

(a) Differentiating the expression for sin , we get cos ·

3

3

√

√

√ 2

4 cos

3

3

11

1

4 3

2

3

= sin = sin =

≈ 656 rads.

= √

, so cos = 1 − and =

=

3

6

6

12

cos

11

1112

= (40 cos 40 sin ) = (40 cos 12 40 sin 12), so sin =

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

CHAPTER 2 PROBLEMS PLUS

(b) By the Law of Cosines, | |2 = ||2 + | |2 − 2 || | | cos

¤

107

⇒

1202 = 402 + | |2 − 2 · 40 | | cos ⇒ | |2 − (80 cos ) | | − 12,800 = 0 ⇒

√

√

√

| | = 1 80 cos ± 6400 cos2 + 51,200 = 40 cos ± 40 cos2 + 8 = 40 cos + 8 + cos2 cm

2

√

[since | | 0]. As a check, note that | | = 160 cm when = 0 and | | = 80 2 cm when = .

2

√

(c) By part (b), the -coordinate of is given by = 40 cos + 8 + cos2 , so

2 cos sin cos

=

= 40 − sin − √

· 12 = −480 sin 1 + √ cms.

2 8 + cos2

8 + cos2

In particular, = 0 cms when = 0 and = −480 cms when =

.

2

13. It seems from the ﬁgure that as approaches the point (0 2) from the right, → ∞ and → 2+ . As approaches the

point (3 0) from the left, it appears that → 3+ and → ∞. So we guess that ∈ (3 ∞) and ∈ (2 ∞). It is

e

more difﬁcult to estimate the range of values for and . We might perhaps guess that ∈ (0 3),

al

and ∈ (−∞ 0) or (−2 0).

In order to actually solve the problem, we implicitly differentiate the equation of the ellipse to ﬁnd the equation of the

2

2

+

=1 ⇒

9

4

2

2 0

4

+

= 0, so 0 = −

. So at the point (0 0 ) on the ellipse, an equation of the

9

4

9

rS

tangent line:

2

2

4 0

0 0

2

+

= 0 + 0 = 1,

( − 0 ) or 40 + 90 = 42 + 90 . This can be written as

0

9 0

9

4

9

4

0 0

+

= 1. because (0 0 ) lies on the ellipse. So an equation of the tangent line is

9

4

Fo

tangent line is − 0 = −

Therefore, the -intercept for the tangent line is given by by 0

9

= 1 ⇔ =

, and the -intercept is given

9

0

0

4

= 1 ⇔ = .

4

0

ot

So as 0 takes on all values in (0 3), takes on all values in (3 ∞), and as 0 takes on all values in (0 2), takes on

At the point (0 0 ) on the ellipse, the slope of the normal line is −

9 0

1

=

, and its

0 (0 0 )

4 0

N

all values in (2 ∞).

equation is − 0 =

9 0

9 0

( − 0 ). So the -intercept for the normal line is given by 0 − 0 =

( − 0 ) ⇒

4 0

4 0

40

50

9 0

90

50

(0 − 0 ) ⇒ = −

+ 0 =

, and the -intercept is given by − 0 =

+ 0 = −

.

9

9

4 0

4

4

So as 0 takes on all values in (0 3), takes on all values in 0 5 , and as 0 takes on all values in (0 2), takes on

3

all values in − 5 0 .

2

= −

15. (a) If the two lines 1 and 2 have slopes 1 and 2 and angles of

inclination 1 and 2 , then 1 = tan 1 and 2 = tan 2 . The triangle in the ﬁgure shows that 1 + + (180◦ − 2 ) = 180◦ and so

= 2 − 1 . Therefore, using the identity for tan( − ), we have tan = tan(2 − 1 ) =

tan 2 − tan 1

2 − 1 and so tan =

.

1 + tan 2 tan 1

1 + 1 2

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

108

¤

CHAPTER 2 PROBLEMS PLUS

(b) (i) The parabolas intersect when 2 = ( − 2)2

⇒ = 1. If = 2 , then 0 = 2, so the slope of the tangent

to = 2 at (1 1) is 1 = 2(1) = 2. If = ( − 2)2 , then 0 = 2( − 2), so the slope of the tangent to

= ( − 2)2 at (1 1) is 2 = 2(1 − 2) = −2. Therefore, tan = so = tan−1

4

3

4

2 − 1

−2 − 2

= and

=

1 + 1 2

1 + 2(−2)

3

≈ 53◦ [or 127◦ ].

(ii) 2 − 2 = 3 and 2 − 4 + 2 + 3 = 0 intersect when 2 − 4 + (2 − 3) + 3 = 0 ⇔ 2( − 2) = 0 ⇒

= 0 or 2, but 0 is extraneous. If = 2, then = ±1. If 2 − 2 = 3 then 2 − 2 0 = 0 ⇒ 0 = and

2 − 4 + 2 + 3 = 0 ⇒ 2 − 4 + 2 0 = 0 ⇒ 0 =

2 = 0, so tan =

= −2 ⇒ ≈ 117◦ . At (2 −1) the slopes are 1 = −2 and 2 = 0

17. Since ∠ = ∠ = , the triangle is isosceles, so

e

0 − (−2)

= 2 ⇒ ≈ 63◦ [or 117◦ ].

1 + (−2)(0)

al

so tan =

0−2

1+2·0

2−

. At (2 1) the slopes are 1 = 2 and

|| = || = . By the Law of Cosines, 2 = 2 + 2 − 2 cos . Hence,

2

=

. Note that as → 0+ , → 0+ (since

2 cos

2 cos

sin = ), and hence →

rS

2 cos = 2 , so =

= . Thus, as is taken closer and closer

2 cos 0

2

→0

sin( + 2) − 2 sin( + ) + sin

2

sin cos 2 + cos sin 2 − 2 sin cos − 2 cos sin + sin

= lim

→0

2 sin (cos 2 − 2 cos + 1) + cos (sin 2 − 2 sin )

= lim

→0

2

ot

19. lim

Fo

to the -axis, the point approaches the midpoint of the radius .

sin (2 cos2 − 1 − 2 cos + 1) + cos (2 sin cos − 2 sin )

→0

2 sin (2 cos )(cos − 1) + cos (2 sin )(cos − 1)

= lim

→0

2

2(cos − 1)[sin cos + cos sin ](cos + 1)

= lim

→0

2 (cos + 1)

2

−2 sin2 [sin( + )] sin( + 0) sin sin( + )

= −2 lim

= −2(1)2

= − sin

·

= lim

→0

→0

2 (cos + 1)

cos + 1 cos 0 + 1

N

= lim

21. = 4 − 22 −

⇒ 0 = 43 − 4 − 1. The equation of the tangent line at = is

− (4 − 22 − ) = (43 − 4 − 1)( − ) or = (43 − 4 − 1) + (−34 + 22 ) and similarly for = . So if at

= and = we have the same tangent line, then 43 − 4 − 1 = 43 − 4 − 1 and −34 + 22 = −34 + 22 . The ﬁrst equation gives 3 − 3 = − ⇒ ( − )(2 + + 2 ) = ( − ). Assuming 6= , we have 1 = 2 + + 2 .

The second equation gives 3(4 − 4 ) = 2(2 − 2 ) ⇒ 3(2 − 2 )(2 + 2 ) = 2(2 − 2 ) which is true if = −.

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

¤

CHAPTER 2 PROBLEMS PLUS

Substituting into 1 = 2 + + 2 gives 1 = 2 − 2 + 2

109

⇒ = ±1 so that = 1 and = −1 or vice versa. Thus,

the points (1 −2) and (−1 0) have a common tangent line.

As long as there are only two such points, we are done. So we show that these are in fact the only two such points.

Suppose that 2 − 2 6= 0. Then 3(2 − 2 )(2 + 2 ) = 2(2 − 2 ) gives 3(2 + 2 ) = 2 or 2 + 2 = 2 .

3

Thus, = (2 + + 2 ) − (2 + 2 ) = 1 −

2

1

2

1

1

= , so =

. Hence, 2 + 2 = , so 94 + 1 = 62

3

3

3

9

3

1

3

0 = 94 − 62 + 1 = (32 − 1)2 . So 32 − 1 = 0 ⇒ 2 =

⇒ 2 =

⇒

1

1

= = 2 , contradicting our assumption

92

3

that 2 6= 2 .

23. Because of the periodic nature of the lattice points, it sufﬁces to consider the points in the 5 × 2 grid shown. We can see that

the minimum value of occurs when there is a line with slope

2

5

which touches the circle centered at (3 1) and the circles

rS

al

e

centered at (0 0) and (5 2).

= − 5 ⇒ 2 +

2

25

4

Fo

To ﬁnd , the point at which the line is tangent to the circle at (0 0), we simultaneously solve 2 + 2 = 2 and

2 = 2

⇒ 2 =

4

29

2

⇒ =

√2

29

, = − √5 . To ﬁnd , we either use symmetry or

29

solve ( − 3)2 + ( − 1)2 = 2 and − 1 = − 5 ( − 3). As above, we get = 3 −

2

√

√

29 + 50 = 6 29 − 8

N

5

1+

√5

29

√2

29

ot

the line is 2 , so =

5

− − √5

29

3−

−

⇔ 58 =

√2

29

=

1+

3−

√

29 ⇔ =

√

10

√

29

√4

29

29

.

58

=

√2

29

, = 1 +

√

29 + 10

2

√

=

5

3 29 − 4

√5

29

. Now the slope of

⇒

So the minimum value of for which any line with slope

intersects circles with radius centered at the lattice points on the plane is =

√

29

58

≈ 0093.

5

=

⇒ =

. The volume of the cone is

5

16

16

2

5

25 2

25 3

2

1

1

, so

=

. Now the rate of

=

= 3 = 3

16

768

256

By similar triangles,

25.

change of the volume is also equal to the difference of what is being added

(2 cm3 min) and what is oozing out (, where is the area of the cone and is a proportionality constant). Thus,

Equating the two expressions for

= 2 − .

10

5(10)

25

= and substituting = 10,

= −03, =

=

, and √

16

8

16

281

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

⇔

2

5

¤

CHAPTER 2 PROBLEMS PLUS

√

125 281

750

=2+

. Solving for gives us

64

256

=

5√

25

25 5 √

281, we get

281 ⇔

(10)2 (−03) = 2 −

·

8

256

8 8

=

256 + 375

√

. To maintain a certain height, the rate of oozing, , must equal the rate of the liquid being poured in;

250 281

Fo

rS

al

e

= 0. Thus, the rate at which we should pour the liquid into the container is

√

256 + 375

25 5 281

256 + 375

√

=

··

·

=

≈ 11204 cm3min

8

8

128

250 281

ot

that is,

N

110

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

3

APPLICATIONS OF DIFFERENTIATION

3.1 Maximum and Minimum Values

1. A function has an absolute minimum at = if () is the smallest function value on the entire domain of , whereas

has a local minimum at if () is the smallest function value when is near .

3. Absolute maximum at , absolute minimum at , local maximum at , local minima at and , neither a maximum nor a

minimum at and .

(6) = 4; local minimum values are (2) = 2 and (1) = (5) = 3.

local maximum at 3, local minima at 2 and 4

Fo

rS

local minimum at 4

9. Absolute maximum at 5, absolute minimum at 2,

al

7. Absolute minimum at 2, absolute maximum at 3,

e

5. Absolute maximum value is (4) = 5; there is no absolute minimum value; local maximum values are (4) = 5 and

(b)

(c)

N

ot

11. (a)

13. (a) Note: By the Extreme Value Theorem,

(b)

must not be continuous; because if it were, it would attain an absolute minimum. c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

111

112

¤

CHAPTER 3

15. () =

1

(3

2

APPLICATIONS OF DIFFERENTIATION

− 1), ≤ 3. Absolute maximum

17. () = 1, ≥ 1. Absolute maximum (1) = 1;

no local maximum. No absolute or local minimum.

(3) = 4; no local maximum. No absolute or local minimum. 19. () = sin , 0 ≤ 2. No absolute or local

21. () = sin , −2 ≤ ≤ 2. Absolute maximum

maximum. Absolute minimum (0) = 0; no local

rS

al

minimum.

e

= 1; no local maximum. Absolute minimum

2

− 2 = −1; no local minimum.

25. () = 1 −

Fo

23. () = 1 + ( + 1)2 , −2 ≤ 5. No absolute or local

no local maximum. No absolute or local minimum.

27. () =

1−

N

ot

maximum. Absolute and local minimum (−1) = 1.

√

. Absolute maximum (0) = 1;

2 − 4

if 0 ≤ 2

if 2 ≤ ≤ 3

Absolute maximum (3) = 2; no local maximum.

29. () = 4 + 1 − 1 2

3

2

⇒ 0 () =

1

3

− .

0 () = 0 ⇒ = 1 . This is the only critical number.

3

No absolute or local minimum.

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

SECTION 3.1

MAXIMUM AND MINIMUM VALUES

¤

113

⇒ 0 () = 62 − 6 − 36 = 6(2 − − 6) = 6( + 2)( − 3).

31. () = 23 − 32 − 36

0 () = 0 ⇔ = −2, 3. These are the only critical numbers.

⇒ 0 () = 43 + 32 + 2 = (42 + 3 + 2). Using the quadratic formula, we see that

33. () = 4 + 3 + 2 + 1

42 + 3 + 2 = 0 has no real solution (its discriminant is negative), so 0 () = 0 only if = 0. Hence, the only critical number is 0.

35. () =

0 () =

−1

2 − + 1

⇒

( 2 − + 1)(1) − ( − 1)(2 − 1)

2 − + 1 − (22 − 3 + 1)

− 2 + 2

(2 − )

=

= 2

= 2

.

( 2 − + 1)2

( 2 − + 1)2

( − + 1)2

( − + 1)2

0 () = 0 ⇒ = 0, 2. The expression 2 − + 1 is never equal to 0, so 0 () exists for all real numbers.

√

=2

39. () = 45 ( − 4)2

⇒

√

=

3

√

−2

√

.

4

4 3

al

0 () = 0 ⇒ 3

⇒ 0 () = 3 −14 − 2 −34 = 1 −34 (312 − 2) =

4

4

4

⇒ = 4 . 0 () does not exist at = 0, so the critical numbers are 0 and 4 .

9

9

2

3

rS

37. () = 34 − 214

e

The critical numbers are 0 and 2.

⇒

0 () = 45 · 2( − 4) + ( − 4)2 · 4 −15 = 1 −15 ( − 4)[5 · · 2 + ( − 4) · 4]

5

5

( − 4)(14 − 16)

2( − 4)(7 − 8)

=

515

515

Fo

=

0 () = 0 ⇒ = 4, 8 . 0 (0) does not exist. Thus, the three critical numbers are 0, 8 , and 4.

7

7

41. () = 2 cos + sin2

⇒ 0 () = −2 sin + 2 sin cos . 0 () = 0 ⇒ 2 sin (cos − 1) = 0 ⇒ sin = 0

ot

or cos = 1 ⇒ = [ an integer] or = 2. The solutions = include the solutions = 2, so the critical

N

numbers are = .

43. A graph of 0 () = 1 +

210 sin is shown. There are 10 zeros

2 − 6 + 10

between −25 and 25 (one is approximately −005). 0 exists everywhere, so has 10 critical numbers.

45. () = 12 + 4 − 2 , [0 5].

0 () = 4 − 2 = 0 ⇔ = 2. (0) = 12, (2) = 16, and (5) = 7.

So (2) = 16 is the absolute maximum value and (5) = 7 is the absolute minimum value.

47. () = 23 − 32 − 12 + 1, [−2 3].

0 () = 62 − 6 − 12 = 6(2 − − 2) = 6( − 2)( + 1) = 0 ⇔

= 2 −1. (−2) = −3, (−1) = 8, (2) = −19, and (3) = −8. So (−1) = 8 is the absolute maximum value and

(2) = −19 is the absolute minimum value. c ° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

¤

114

CHAPTER 3

APPLICATIONS OF DIFFERENTIATION

49. () = 34 − 43 − 122 + 1, [−2 3].

0 () = 123 − 122 − 24 = 12(2 − − 2) = 12( + 1)( − 2) = 0 ⇔

= −1, 0, 2. (−2) = 33, (−1) = −4, (0) = 1, (2) = −31, and (3) = 28. So (−2) = 33 is the absolute maximum value and (2) = −31 is the absolute minimum value.

1

1

2 − 1

( + 1)( − 1)

=

= 0 ⇔ = ±1, but = −1 is not in the given

, [02 4]. 0 () = 1 − 2 =

2

2

51. () = +

interval, [02 4]. 0 () does not exist when = 0, but 0 is not in the given interval, so 1 is the only critical nuumber.

(02) = 52, (1) = 2, and (4) = 425. So (02) = 52 is the absolute maximum value and (1) = 2 is the absolute minimum value.

53. () =

√

4 − 2 , [−1 2].

√

√

2 = 2 is the absolute maximum value and (−1) = − 3 is the absolute minimum value.

rS

(2) = 0. So

al

e

√

−2

−2 + (4 − 2 )

4 − 22

√

0 () = · 1 (4 − 2 )−12 (−2) + (4 − 2 )12 · 1 = √

+ 4 − 2 =

= √

.

2

2

2

4−

4−

4 − 2

√

√

0 () = 0 ⇒ 4 − 22 = 0 ⇒ 2 = 2 ⇒ = ± 2, but = − 2 is not in the given interval, [−1 2].

√

√

0 () does not exist if 4 − 2 = 0 ⇒ = ±2, but −2 is not in the given interval. (−1) = − 3, 2 = 2, and

55. () = 2 cos + sin 2, [0, 2].

So ( ) =

6

3

2

Fo

0 () = −2 sin + cos 2 · 2 = −2 sin + 2(1 − 2 sin2 ) = −2(2 sin2 + sin − 1) = −2(2 sin − 1)(sin + 1).

√

√

√

0 () = 0 ⇒ sin = 1 or sin = −1 ⇒ = . (0) = 2, ( ) = 3 + 1 3 = 3 3 ≈ 260, and ( ) = 0.

2

6

6

2

2

2

√

3 is the absolute maximum value and ( ) = 0 is the absolute minimum value.

2

57. () = (1 − ) , 0 ≤ ≤ 1, 0, 0.

ot

0 () = · (1 − )−1 (−1) + (1 − ) · −1 = −1 (1 − )−1 [ · (−1) + (1 − ) · ]

N

= −1 (1 − )−1 ( − − )

At the endpoints, we have (0) = (1) = 0 [the minimum value of ]. In the interval (0 1), 0 () = 0 ⇔ =

+

So

59. (a)

=

+

+

=

1−

+

=

( + )

+−

+

=

+

·

=

.

( + ) ( + )

( + )+

is the absolute maximum value.

( + )+

From the graph, it appears that the absolute maximum value is about

(−077) = 219, and the absolute minimum value is about (077) = 181.

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

SECTION 3.1

MAXIMUM AND MINIMUM VALUES

¤

115

(b) () = 5 − 3 + 2 ⇒ 0 () = 54 − 32 = 2 (52 − 3). So 0 () = 0 ⇒ = 0, ± 3 .

5

5

3

3 2 3

3

3

3

3

3

− 5 = − 5 − − 5 +2=− 5

5 + 5

5 +2

3

9

6

= 3 − 25

+ 2 = 25 3 + 2 (maximum)

5

5

5

3

6

= − 25 3 + 2 (minimum). and similarly,

5

5

61. (a)

From the graph, it appears that the absolute maximum value is about

(075) = 032, and the absolute minimum value is (0) = (1) = 0; that is, at both endpoints.

√

− 2

⇒ 0 () = ·

√

1 − 2

( − 22 ) + (2 − 22 )

3 − 42

√

√

+ − 2 =

= √

.

2 − 2

2 − 2

2 − 2

e

(b) () =

63. The density is deﬁned as =

mass

1000

=

(in gcm3 ). But a critical point of will also be a critical point of volume ( )

= −1000 −2 and is never 0], and is easier to differentiate than .

Fo

[since

rS

al

So 0 () = 0 ⇒ 3 − 42 = 0 ⇒ (3 − 4) = 0 ⇒ = 0 or 3 .

4

√

2

3

(0) = (1) = 0 (minimum), and 3 = 3 3 − 3 = 3 16 = 3163 (maximum).

4

4

4

4

4

( ) = 99987 − 006426 + 00085043 2 − 00000679 3

⇒ 0 ( ) = −006426 + 00170086 − 00002037 2 .

ot

Setting this equal to 0 and using the quadratic formula to ﬁnd , we get

√

−00170086 ± 001700862 − 4 · 00002037 · 006426

=

≈ 39665◦ C or 795318◦ C. Since we are only interested

2(−00002037)

in the region 0◦ C ≤ ≤ 30◦ C, we check the density at the endpoints and at 39665◦ C: (0) ≈

1000

1000

≈ 099625; (39665) ≈

≈ 1000255. So water has its maximum density at

10037628

9997447

N

(30) ≈

1000

≈ 100013;

99987

about 39665◦ C.

65. Let = −0000 032 37, = 0000 903 7, = −0008 956, = 003629, = −004458, and = 04074.

Then () = 5 + 4 + 3 + 2 + + and 0 () = 54 + 43 + 32 + 2 + .

We now apply the Closed Interval Method to the continuous function on the interval 0 ≤ ≤ 10. Since 0 exists for all , the only critical numbers of occur when 0 () = 0. We use a rootﬁnder on a CAS (or a graphing device) to ﬁnd that

0 () = 0 when 1 ≈ 0855, 2 ≈ 4618, 3 ≈ 7292, and 4 ≈ 9570. The values of at these critical numbers are

(1 ) ≈ 039, (2 ) ≈ 043645, (3 ) ≈ 0427, and (4 ) ≈ 043641. The values of at the endpoints of the interval are

(0) ≈ 041 and (10) ≈ 0435. Comparing the six numbers, we see that sugar was most expensive at 2 ≈ 4618

(corresponding roughly to March 1998) and cheapest at 1 ≈ 0855 (June 1994).

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

¤

116

CHAPTER 3

APPLICATIONS OF DIFFERENTIATION

⇒ 0 () = 20 − 32 . 0 () = 0 ⇒ (20 − 3) = 0 ⇒

3

= 0 or 2 0 (but 0 is not in the interval). Evaluating at 1 0 , 2 0 , and 0 , we get 1 0 = 1 0 , 2 0 =

3

2

3

2

8

3

67. (a) () = (0 − )2 = 0 2 − 3

and (0 ) = 0. Since

4

27

3

4

0 ,

27

1 , attains its maximum value at = 2 0 . This supports the statement in the text.

8

3

(b) From part (a), the maximum value of is

69. () = 101 + 51 + + 1

3

4

0 .

27

(c)

⇒ 0 () = 101100 + 5150 + 1 ≥ 1 for all , so 0 () = 0 has no solution. Thus, ()

e

has no critical number, so () can have no local maximum or minimum.

al

71. If has a local minimum at , then () = − () has a local maximum at , so 0 () = 0 by the case of Fermat’s Theorem

proved in the text. Thus, 0 () = − 0 () = 0.

1. () = 5 − 12 + 32 , [1, 3].

rS

3.2 The Mean Value Theorem

Since is a polynomial, it is continuous and differentiable on R, so it is continuous on [1 3]

Fo

and differentiable on (1 3). Also (1) = −4 = (3). 0 () = 0 ⇔ −12 + 6 = 0 ⇔ = 2, which is in the open interval (1 3), so = 2 satisﬁes the conclusion of Rolle’s Theorem.

3. () =

√

− 1 , [0 9]. , being the difference of a root function and a polynomial, is continuous and differentiable

3

on [0 ∞), so it is continuous on [0 9] and differentiable on (0 9). Also, (0) = 0 = (9). 0 () = 0 ⇔

√

√

3

1

1

√ − =0 ⇔ 2 =3 ⇔

=

3

2

ot

2

⇒ =

9

9

, which is in the open interval (0 9), so = satisﬁes the

4

4

N

conclusion of Rolle’s Theorem.

5. () = 1 − 23 .

(−1) = 1 − (−1)23 = 1 − 1 = 0 = (1). 0 () = − 2 −13 , so 0 () = 0 has no solution. This

3

does not contradict Rolle’s Theorem, since 0 (0) does not exist, and so is not differentiable on (−1 1).

7. 0 () =

0 () =

3−0

3

(8) − (0)

=

= . It appears that

8−0

8

8

3

8

when ≈ 03, 3, and 63.

9. () = 22 − 3 + 1, [0 2].

differentiable on R. 0 () = is in (0 2)

is continuous on [0 2] and differentiable on (0 2) since polynomials are continuous and

() − ()

−

⇔ 4 − 3 =

(2) − (0)

3−1

=

= 1 ⇔ 4 = 4 ⇔ = 1, which

2−0

2

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

SECTION 3.2

11. () =

√

3

, [0 1].

THE MEAN VALUE THEOREM

323 = 1 ⇔ 23 =

1

1

() − ()

(1) − (0)

1−0

⇔

⇔

=

=

−

1−0

1

323

323

√

√

1 3

1

1

⇔ 2 = 3 = 27 ⇔ = ± 27 = ± 93 , but only 93 is in (0 1).

1

3

√

(4) − (0)

, [0 4]. 0 () =

4−0

1

1

√ =

2

2

⇔

117

is continuous on R and differentiable on (−∞ 0) ∪ (0 ∞), so is continuous on [0 1]

and differentiable on (0 1). 0 () =

13. () =

¤

⇔

1

2−0

√ =

4

2

⇔

⇔

√

= 1 ⇔ = 1. The secant line and the tangent line

are parallel.

1

1

−2

−

=

·3 ⇒

12

(−2)2

( − 3)3

⇒ ( − 3)3 = −8 ⇒ − 3 = −2 ⇒ = 1, which is not in the open interval (1 4). This does not

al

−6

3

=

4

( − 3)3

⇒ 0 () = −2 ( − 3)−3 . (4) − (1) = 0 ()(4 − 1) ⇒

e

15. () = ( − 3)−2

contradict the Mean Value Theorem since is not continuous at = 3.

rS

17. Let () = 2 + cos . Then (−) = −2 − 1 0 and (0) = 1 0. Since is the sum of the polynomial 2 and the

trignometric function cos , is continuous and differentiable for all . By the Intermediate Value Theorem, there is a number

in (− 0) such that () = 0. Thus, the given equation has at least one real root. If the equation has distinct real roots and

Fo

with , then () = () = 0. Since is continuous on [ ] and differentiable on ( ), Rolle’s Theorem implies that there is a number in ( ) such that 0 () = 0. But 0 () = 2 − sin 0 since sin ≤ 1. This contradiction shows that the given equation can’t have two distinct real roots, so it has exactly one root.

ot

19. Let () = 3 − 15 + for in [−2 2]. If has two real roots and in [−2 2], with , then () = () = 0. Since

the polynomial is continuous on [ ] and differentiable on ( ), Rolle’s Theorem implies that there is a number in ( )

N

such that 0 () = 0. Now 0 () = 32 − 15. Since is in ( ), which is contained in [−2 2], we have || 2, so 2 4.

It follows that 32 − 15 3 · 4 − 15 = −3 0. This contradicts 0 () = 0, so the given equation can’t have two real roots in [−2 2]. Hence, it has at most one real root in [−2 2].

21. (a) Suppose that a cubic polynomial () has roots 1 2 3 4 , so (1 ) = (2 ) = (3 ) = (4 ).

By Rolle’s Theorem there are numbers 1 , 2 , 3 with 1 1 2 , 2 2 3 and 3 3 4 and

0 (1 ) = 0 (2 ) = 0 (3 ) = 0. Thus, the second-degree polynomial 0 () has three distinct real roots, which is impossible. (b) We prove by induction that a polynomial of degree has at most real roots. This is certainly true for = 1. Suppose that the result is true for all polynomials of degree and let () be a polynomial of degree + 1. Suppose that () has more than + 1 real roots, say 1 2 3 · · · +1 +2 . Then (1 ) = (2 ) = · · · = (+2 ) = 0.

By Rolle’s Theorem there are real numbers 1 +1 with 1 1 2 +1 +1 +2 and

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

118

¤

CHAPTER 3

APPLICATIONS OF DIFFERENTIATION

0 (1 ) = · · · = 0 (+1 ) = 0. Thus, the th degree polynomial 0 () has at least + 1 roots. This contradiction shows that () has at most + 1 real roots.

23. By the Mean Value Theorem, (4) − (1) = 0 ()(4 − 1) for some ∈ (1 4). But for every ∈ (1 4) we have

0 () ≥ 2. Putting 0 () ≥ 2 into the above equation and substituting (1) = 10, we get

(4) = (1) + 0 ()(4 − 1) = 10 + 3 0 () ≥ 10 + 3 · 2 = 16. So the smallest possible value of (4) is 16.

25. Suppose that such a function exists. By the Mean Value Theorem there is a number 0 2 with

0 () =

5

(2) − (0)

= . But this is impossible since 0 () ≤ 2

2−0

2

27. We use Exercise 26 with () =

5

2

for all , so no such function can exist.

√

1 + , () = 1 + 1 , and = 0. Notice that (0) = 1 = (0) and

2

√

1

1

√

= 0 () for 0. So by Exercise 26, () () ⇒

1 + 1 + 1 for 0.

2

2

1+

√

√

Another method: Apply the Mean Value Theorem directly to either () = 1 + 1 − 1 + or () = 1 + on [0 ].

2

2

al

e

0 () =

29. Let () = sin and let . Then () is continuous on [ ] and differentiable on ( ). By the Mean Value Theorem,

rS

there is a number ∈ ( ) with sin − sin = () − () = 0 ()( − ) = (cos )( − ). Thus,

|sin − sin | ≤ |cos | | − | ≤ | − |. If , then |sin − sin | = |sin − sin | ≤ | − | = | − |. If = , both sides of the inequality are 0.

Fo

31. For 0, () = (), so 0 () = 0 (). For 0, 0 () = (1)0 = −12 and 0 () = (1 + 1)0 = −12 , so

again 0 () = 0 (). However, the domain of () is not an interval [it is (−∞ 0) ∪ (0 ∞)] so we cannot conclude that

− is constant (in fact it is not).

33. Let () and () be the position functions of the two runners and let () = () − (). By hypothesis,

ot

(0) = (0) − (0) = 0 and () = () − () = 0, where is the ﬁnishing time. Then by the Mean Value Theorem,

N

there is a time , with 0 , such that 0 () =

() − (0)

. But () = (0) = 0, so 0 () = 0. Since

−0

0 () = 0 () − 0 () = 0, we have 0 () = 0 (). So at time , both runners have the same speed 0 () = 0 ().

3.3 How Derivatives Affect the Shape of a Graph

1. (a) is increasing on (1 3) and (4 6).

(c) is concave upward on (0 2).

(b) is decreasing on (0 1) and (3 4).

(d) is concave downward on (2 4) and (4 6).

(e) The point of inﬂection is (2 3).

3. (a) Use the Increasing/Decreasing (I/D) Test.

(b) Use the Concavity Test.

(c) At any value of where the concavity changes, we have an inﬂection point at ( ()).

5. (a) Since 0 () 0 on (1 5), is increasing on this interval. Since 0 () 0 on (0 1) and (5 6), is decreasing on these

intervals. c ° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

SECTION 3.3

HOW DERIVATIVES AFFECT THE SHAPE OF A GRAPH

¤

119

(b) Since 0 () = 0 at = 1 and 0 changes from negative to positive there, changes from decreasing to increasing and has a local minimum at = 1. Since 0 () = 0 at = 5 and 0 changes from positive to negative there, changes from increasing to decreasing and has a local maximum at = 5.

7. (a) There is an IP at = 3 because the graph of changes from CD to CU there. There is an IP at = 5 because the graph

of changes from CU to CD there.

(b) There is an IP at = 2 and at = 6 because 0 () has a maximum value there, and so 00 () changes from positive to negative there. There is an IP at = 4 because 0 () has a minimum value there and so 00 () changes from negative to positive there.

(c) There is an inﬂection point at = 1 because 00 () changes from negative to positive there, and so the graph of changes from concave downward to concave upward. There is an inﬂection point at = 7 because 00 () changes from positive to

⇒ 0 () = 62 + 6 − 36 = 6(2 + − 6) = 6( + 3)( − 2).

al

9. (a) () = 23 + 32 − 36

e

negative there, and so the graph of changes from concave upward to concave downward.

We don’t need to include the “6” in the chart to determine the sign of 0 ().

−2

0 ()

−

−

+

+

Interval

+

+

rS

+3

−3

−3 2

+

2

−

−

increasing on (−∞ −3) decreasing on (−3 2) increasing on (2 ∞)

Fo

(b) changes from increasing to decreasing at = −3 and from decreasing to increasing at = 2. Thus, (−3) = 81 is a local maximum value and (2) = −44 is a local minimum value.

ot

(c) 0 () = 62 + 6 − 36 ⇒ 00 () = 12 + 6. 00 () = 0 at = − 1 , 00 () 0 ⇔ − 1 , and

2

2

1

00

1

() 0 ⇔ − 2 . Thus, is concave upward on − 2 ∞ and concave downward on −∞ − 1 . There is an

2

inﬂection point at − 1 − 1 = − 1 37 .

2

2

2 2

⇒ 0 () = 43 − 4 = 4 2 − 1 = 4( + 1)( − 1).

N

11. (a) () = 4 − 22 + 3

Interval

+1

−1

0 ()

−1

−

−

−

−

decreasing on (−∞ −1)

01

+

+

+

−

decreasing on (0 1)

1

−

−1 0

+

−

+

−

+

+

+

increasing on (−1 0) increasing on (1 ∞)

(b) changes from increasing to decreasing at = 0 and from decreasing to increasing at = −1 and = 1. Thus,

(0) = 3 is a local maximum value and (±1) = 2 are local minimum values.

√

√

√

√

(c) 00 () = 122 − 4 = 12 2 − 1 = 12 + 1 3 − 1 3 . 00 () 0 ⇔ −1 3 or 1 3 and

3

√

√

√

√

00 () 0 ⇔ −1 3 1 3. Thus, is concave upward on −∞ − 33 and

33 ∞ and concave

√

√

√

downward on − 33 33 . There are inﬂection points at ± 33 22 .

9

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

120

¤

CHAPTER 3

APPLICATIONS OF DIFFERENTIATION

13. (a) () = sin + cos , 0 ≤ ≤ 2.

0 () = cos − sin = 0 ⇒ cos = sin ⇒ 1 =

sin cos

⇒

Thus, 0 () 0 ⇔ cos − sin 0 ⇔ cos sin ⇔ 0 or

4

5

5

2 and 0 () 0 ⇔ cos sin ⇔ 5 . So is increasing on 0 4 and 4 2 and

4

4

4

is decreasing on 5 .

4

4 tan = 1 ⇒ =

4

or

5

4 .

(b) changes from increasing to decreasing at = local maximum value and

5

4

4

and from decreasing to increasing at =

3

4

or

√

2 is a

Thus,

7

.

4

Divide the interval

√

= − 2 is a local minimum value.

(c) 00 () = − sin − cos = 0 ⇒ − sin = cos ⇒ tan = −1 ⇒ =

5

.

4

4

=

(0 2) into subintervals with these numbers as endpoints and complete a second derivative chart.

15. () = 1 + 32 − 23

4

0 and 7 0 .

4

1

2

√

30

e

00 () = 1 0

00 11 = 1 −

6

2

Concavity downward upward

al

3

00 () = − sin − cos

00 = −1 0

2

downward

rS

There are inﬂection points at

Interval

3

0 4

3 7

4

4

7

2

4

⇒ 0 () = 6 − 62 = 6(1 − ).

Fo

First Derivative Test: 0 () 0 ⇒ 0 1 and 0 () 0 ⇒ 0 or 1. Since 0 changes from negative to positive at = 0, (0) = 1 is a local minimum value; and since 0 changes from positive to negative at = 1, (1) = 2 is a local maximum value.

Second Derivative Test: 00 () = 6 − 12. 0 () = 0 ⇔ = 0 1. 00 (0) = 6 0 ⇒ (0) = 1 is a local

ot

minimum value. 00 (1) = −6 0 ⇒ (1) = 2 is a local maximum value.

Preference: For this function, the two tests are equally easy.

N

√

√

1

− 4 ⇒ 0 () = −12 −

2

√

First Derivative Test: 2 4 − 1 0 ⇒

17. () =

√

1 −34

1

24 −1

√

= −34 (214 − 1) =

4

4

4

4 3

Since 0 changes from negative to positive at =

1

,

16

1

,

16

so 0 () 0 ⇒

1

( 16 ) =

1

4

−

1

2

1

16

and 0 () 0 ⇒ 0

1

.

16

= − 1 is a local minimum value.

4

1

3

1

3

Second Derivative Test: 00 () = − −32 + −74 = − √ + √ .

4

4

16

4 3

16 7

1

1

1

0 () = 0 ⇔ = 16 . 00 16 = −16 + 24 = 8 0 ⇒ 16 = − 1 is a local minimum value.

4

Preference: The First Derivative Test may be slightly easier to apply in this case.

19. (a) By the Second Derivative Test, if 0 (2) = 0 and 00 (2) = −5 0, has a local maximum at = 2.

(b) If 0 (6) = 0, we know that has a horizontal tangent at = 6. Knowing that 00 (6) = 0 does not provide any additional information since the Second Derivative Test fails. For example, the ﬁrst and second derivatives of = ( − 6)4 , c ° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

SECTION 3.3

HOW DERIVATIVES AFFECT THE SHAPE OF A GRAPH

¤

121

= −( − 6)4 , and = ( − 6)3 all equal zero for = 6, but the ﬁrst has a local minimum at = 6, the second has a local maximum at = 6, and the third has an inﬂection point at = 6.

⇒ horizontal tangents at = 0, 2, 4.

21. 0 (0) = 0 (2) = 0 (4) = 0

0 () 0 if 0 or 2 4 ⇒ is increasing on (−∞ 0) and (2 4).

0 () 0 if 0 2 or 4 ⇒ is decreasing on (0 2) and (4 ∞).

00 () 0 if 1 3 ⇒ is concave upward on (1 3).

00 () 0 if 1 or 3 ⇒ is concave downward on (−∞ 1) and (3 ∞). There are inﬂection points when = 1 and 3.

23. 0 () 0 if || 2

⇒ is increasing on (−2 2).

0 (−2) = 0 ⇒ horizontal tangent at

= −2. lim | 0 ()| = ∞ ⇒ there is a vertical

→2

al

and (2 ∞).

e

0 () 0 if || 2 ⇒ is decreasing on (−∞ −2)

rS

asymptote or vertical tangent (cusp) at = 2. 00 () 0 if 6= 2 ⇒ is concave upward on (−∞ 2) and (2 ∞).

25. The function must be always decreasing (since the ﬁrst derivative is always

negative) and concave downward (since the second derivative is always

Fo

negative).

ot

27. (a) is increasing where 0 is positive, that is, on (0 2), (4 6), and (8 ∞); and decreasing where 0 is negative, that is, on

(2 4) and (6 8).

N

(b) has local maxima where 0 changes from positive to negative, at = 2 and at = 6, and local minima where 0 changes from negative to positive, at = 4 and at = 8.

(c) is concave upward (CU) where 0 is increasing, that is, on (3 6) and (6 ∞), and concave downward (CD) where 0 is decreasing, that is, on (0 3).

(d) There is a point of inﬂection where changes from

(e)

being CD to being CU, that is, at = 3.

29. (a) () = 3 − 12 + 2

⇒ 0 () = 32 − 12 = 3(2 − 4) = 3( + 2)( − 2). 0 () 0 ⇔ −2 or 2

and 0 () 0 ⇔ −2 2. So is increasing on (−∞ −2) and (2 ∞) and is decreasing on (−2 2).

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

122

¤

CHAPTER 3

APPLICATIONS OF DIFFERENTIATION

(b) changes from increasing to decreasing at = −2, so (−2) = 18 is a local maximum value. changes from decreasing to increasing at = 2, so (2) = −14 is a local minimum value.

(c) 00 () = 6. 00 () = 0 ⇔ = 0. 00 () 0

(d)

on (0 ∞) and 00 () 0 on (−∞ 0). So is concave upward on (0 ∞) and is concave downward on (−∞ 0). There is an inﬂection point at (0 2).

31. (a) () = 2 + 22 − 4

⇒ 0 () = 4 − 43 = 4(1 − 2 ) = 4(1 + )(1 − ). 0 () 0 ⇔ −1 or

0 1 and 0 () 0 ⇔ −1 0 or 1. So is increasing on (−∞ −1) and (0 1) and is decreasing

e

on (−1 0) and (1 ∞).

al

(b) changes from increasing to decreasing at = −1 and = 1, so (−1) = 3 and (1) = 3 are local maximum values.

changes from decreasing to increasing at = 0, so (0) = 2 is a local minimum value.

(d)

Fo

rS

(c) 00 () = 4 − 122 = 4(1 − 32 ). 00 () = 0 ⇔ 1 − 32 = 0 ⇔

√

√

√

2 = 1 ⇔ = ±1 3. 00 () 0 on −1 3 1 3 and 00 () 0

3

√

√

on −∞ −1 3 and 1 3 ∞ . So is concave upward on

√

√

√

−1 3 1 3 and is concave downward on −∞ −1 3 and

√

√

1 3 ∞ . ±1 3 = 2 + 2 − 1 = 23 . There are points of inﬂection

3

9

9

√ 23

at ±1 3 9 .

⇒ 0 () = 5( + 1)4 − 5. 0 () = 0 ⇔ 5( + 1)4 = 5 ⇔ ( + 1)4 = 1 ⇒

ot

33. (a) () = ( + 1)5 − 5 − 2

( + 1)2 = 1 ⇒ + 1 = 1 or + 1 = −1 ⇒ = 0 or = −2. 0 () 0 ⇔ −2 or 0 and

N

0 () 0 ⇔ −2 0. So is increasing on (−∞ −2) and (0 ∞) and is decreasing on (−2 0).

(b) (−2) = 7 is a local maximum value and (0) = −1 is a local minimum value.

(d)

(c) 00 () = 20( + 1)3 = 0 ⇔ = −1. 00 () 0 ⇔ −1 and

00 () 0 ⇔ −1, so is CU on (−1 ∞) and is CD on (−∞ −1).

There is a point of inﬂection at (−1 (−1)) = (−1 3).

√

35. (a) () = 6 −

⇒

0 () = · 1 (6 − )−12 (−1) + (6 − )12 (1) = 1 (6 − )−12 [− + 2(6 − )] =

2

2

−3 + 12

√

.

2 6−

0 () 0 ⇔ −3 + 12 0 ⇔ 4 and 0 () 0 ⇔ 4 6. So is increasing on (−∞ 4) and is decreasing on (4 6). c ° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

SECTION 3.3

HOW DERIVATIVES AFFECT THE SHAPE OF A GRAPH

¤

123

√

(b) changes from increasing to decreasing at = 4, so (4) = 4 2 is a local maximum value. There is no local minimum value. (c) 0 () = − 3 ( − 4)(6 − )−12 ⇒

2

00

() = − 3 ( − 4) − 1 (6 − )−32 (−1) + (6 − )−12 (1)

2

2

(d)

3 1

3( − 8)

= − · (6 − )−32 [( − 4) + 2(6 − )] =

2 2

4(6 − )32

00 () 0 on (−∞ 6), so is CD on (−∞ 6). There is no inﬂection point.

⇒ 0 () = 4 13 + 4 −23 = 4 −23 ( + 1) =

3

3

3

37. (a) () = 13 ( + 4) = 43 + 413

4( + 1)

√

. 0 () 0 if

3

3 2

−1 0 or 0 and 0 () 0 for −1, so is increasing on (−1 ∞) and is decreasing on (−∞ −1).

(d)

4( − 2)

√

.

3

9 5

al

(c) 00 () = 4 −23 − 8 −53 = 4 −53 ( − 2) =

9

9

9

e

(b) (−1) = −3 is a local minimum value.

00 () 0 for 0 2 and 00 () 0 for 0 and 2, so is

39. (a) () = 2 cos + cos2 , 0 ≤ ≤ 2

rS

concave downward on (0 2) and concave upward on (−∞ 0) and (2 ∞).

√

There are inﬂection points at (0 0) and 2 6 3 2 ≈ (2 756).

⇒ 0 () = −2 sin + 2 cos (− sin ) = −2 sin (1 + cos ).

Fo

0 () = 0 ⇔ = 0 and 2. 0 () 0 ⇔ 2 and 0 () 0 ⇔ 0 . So is increasing on ( 2) and is decreasing on (0 ).

(b) () = −1 is a local minimum value.

ot

(c) 0 () = −2 sin (1 + cos ) ⇒

00 () = −2 sin (− sin ) + (1 + cos )(−2 cos ) = 2 sin2 − 2 cos − 2 cos2

N

= 2(1 − cos2 ) − 2 cos − 2 cos2 = −4 cos2 − 2 cos + 2

= −2(2 cos2 + cos − 1) = −2(2 cos − 1)(cos + 1)

(d)

Since −2(cos + 1) 0 [for 6= ], 00 () 0 ⇒ 2 cos − 1 0 ⇒ cos 1 ⇒ 5 and

2

3

3

5

00

1

5

() 0 ⇒ cos 2 ⇒ 0 3 or 3 2. So is CU on 3 3 and is CD on 0 3 and

5

5

= 3 4 and 5 5 = 5 5 .

3 2 . There are points of inﬂection at 3 3

3

3

3 4

41. The nonnegative factors ( + 1)2 and ( − 6)4 do not affect the sign of 0 () = ( + 1)2 ( − 3)5 ( − 6)4 .

So 0 () 0 ⇒ ( − 3)5 0 ⇒ − 3 0 ⇒ 3. Thus, is increasing on the interval (3 ∞). c ° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

124

¤

CHAPTER 3

APPLICATIONS OF DIFFERENTIATION

43. (a)

From the graph, we get an estimate of (1) ≈ 141 as a local maximum value, and no local minimum value.

1−

.

(2 + 1)32

√

2

0 () = 0 ⇔ = 1. (1) = √2 = 2 is the exact value.

+1

() = √

2 + 1

⇒ 0 () =

(b) From the graph in part (a), increases most rapidly somewhere between = − 1 and = − 1 . To ﬁnd the exact value,

2

4 we need to ﬁnd the maximum value of 0 , which we can do by ﬁnding the critical numbers of 0 .

√

√

3 + 17

22 − 3 − 1

3 ± 17

00 () =

. = corresponds to the minimum value of 0 .

=0 ⇔ =

4

4

(2 + 1)52

The maximum value of 0 occurs at =

1

2

√

4

17

≈ −028.

cos 2 ⇒ 0 () = − sin − sin 2 ⇒ 00 () = − cos − 2 cos 2

e

45. () = cos +

3−

(a)

al

From the graph of , it seems that is CD on (0 1), CU on (1 25), CD on

(25 37), CU on (37 53), and CD on (53 2). The points of inﬂection

rS

appear to be at (1 04), (25 −06), (37 −06), and (53 04).

(b)

From the graph of 00 (and zooming in near the zeros), it seems that is CD

Fo

on (0 094), CU on (094 257), CD on (257 371), CU on (371 535),

and CD on (535 2). Reﬁned estimates of the inﬂection points are

ot

(094 044), (257 −063), (371 −063), and (535 044).

4 + 3 + 1

. In Maple, we deﬁne and then use the command

2 + + 1

47. () = √

N

plot(diff(diff(f,x),x),x=-2..2);. In Mathematica, we deﬁne and then use Plot[Dt[Dt[f,x],x],{x,-2,2}]. We see that 00 0 for

−06 and 00 [≈ 003] and 00 0 for −06 00. So is CU on (−∞ −06) and (00 ∞) and CD on (−06 00).

49. (a) The rate of increase of the population is initially very small, then gets larger until it reaches a maximum at about

= 8 hours, and decreases toward 0 as the population begins to level off.

(b) The rate of increase has its maximum value at = 8 hours.

(c) The population function is concave upward on (0 8) and concave downward on (8 18).

(d) At = 8, the population is about 350, so the inﬂection point is about (8 350).

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

SECTION 3.3

HOW DERIVATIVES AFFECT THE SHAPE OF A GRAPH

¤

125

51. Most students learn more in the third hour of studying than in the eighth hour, so (3) − (2) is larger than (8) − (7).

In other words, as you begin studying for a test, the rate of knowledge gain is large and then starts to taper off, so 0 () decreases and the graph of is concave downward.

⇒ 0 () = 32 + 2 + .

53. () = 3 + 2 + +

We are given that (1) = 0 and (−2) = 3, so (1) = + + + = 0 and

(−2) = −8 + 4 − 2 + = 3. Also 0 (1) = 3 + 2 + = 0 and

0 (−2) = 12 − 4 + = 0 by Fermat’s Theorem. Solving these four equations, we get

= 2 , = 1 , = − 4 , = 7 , so the function is () = 1 23 + 32 − 12 + 7 .

9

3

3

9

9

1

0 ( √3 ) = 0 ⇒ 1 +

√

√

⇒ 0 () = 32 + 2 + . has the local minimum value − 2 3 at = 1 3, so

9

2

√

3

√

1

( √3 ) = − 2 3

9

+ = 0 (1) and

⇒

1

9

√

√

√

3 + 1 + 1 3 = − 2 3 (2).

3

3

9

e

55. (a) () = 3 + 2 +

2

3

al

Rewrite the system of equations as

√

3 +

+

(3)

(4)

rS

1

3

= −1

√

√

1

3 = − 1 3

3

3

√ and then multiplying (4) by −2 3 gives us the system

√

3 + = −1

√

− 2 3 − 2 = 2

3

Fo

2

3

Adding the equations gives us − = 1 ⇒ = −1. Substituting −1 for into (3) gives us

√

√

2

3 − 1 = −1 ⇒ 2 3 = 0 ⇒ = 0. Thus, () = 3 − .

3

3

ot

(b) To ﬁnd the smallest slope, we want to ﬁnd the minimum of the slope function, 0 , so we’ll ﬁnd the critical numbers of 0 . () = 3 − ⇒ 0 () = 32 − 1 ⇒ 00 () = 6. 00 () = 0 ⇔ = 0.

N

At = 0, = 0, 0 () = −1, and 00 changes from negative to positive. Thus, we have a minimum for 0 and

− 0 = −1( − 0), or = −, is the tangent line that has the smallest slope.

57. = sin

⇒ 0 = cos + sin ⇒ 00 = − sin + 2 cos . 00 = 0 ⇒ 2 cos = sin [which is ] ⇒

(2 cos )2 = ( sin )2 cos2 (4 + 2 ) = 2

⇒ 4 cos2 = 2 sin2 ⇒ 4 cos2 = 2 (1 − cos2 ) ⇒ 4 cos2 + 2 cos2 = 2

⇒ 4 cos2 (2 + 4) = 42

⇒

⇒ 2 (2 + 4) = 42 since = 2 cos when 00 = 0.

59. (a) Since and are positive, increasing, and CU on with 00 and 00 never equal to 0, we have 0, 0 ≥ 0, 00 0,

0, 0 ≥ 0, 00 0 on . Then ( )0 = 0 + 0

⇒ ()00 = 00 + 2 0 0 + 00 ≥ 00 + 00 0 on

⇒

is CU on .

(b) In part (a), if and are both decreasing instead of increasing, then 0 ≤ 0 and 0 ≤ 0 on , so we still have 2 0 0 ≥ 0 on . Thus, ( )00 = 00 + 2 0 0 + 00 ≥ 00 + 00 0 on

⇒ is CU on as in part (a).

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

126

¤

CHAPTER 3

APPLICATIONS OF DIFFERENTIATION

(c) Suppose is increasing and is decreasing [with and positive and CU]. Then 0 ≥ 0 and 0 ≤ 0 on , so 2 0 0 ≤ 0 on and the argument in parts (a) and (b) fails.

Example 1.

= (0 ∞), () = 3 , () = 1. Then ( )() = 2 , so ( )0 () = 2 and

()00 () = 2 0 on . Thus, is CU on .

Example 2.

Example 3.

√

√

√

= (0 ∞), () = 4 , () = 1. Then ( )() = 4 , so ()0 () = 2 and

√

()00 () = −1 3 0 on . Thus, is CD on .

= (0 ∞), () = 2 , () = 1. Thus, ( )() = , so is linear on .

61. () = tan −

⇒ 0 () = sec2 − 1 0 for 0

on 0 . Thus, () (0) = 0 for 0

2

2

2

since sec2 1 for 0

2.

So is increasing

⇒ tan − 0 ⇒ tan for 0

2.

⇒ 0 () = 32 + 2 + ⇒ 00 () = 6 + 2.

e

63. Let the cubic function be () = 3 + 2 + +

al

So is CU when 6 + 2 0 ⇔ −(3), CD when −(3), and so the only point of inﬂection occurs when = −(3). If the graph has three -intercepts 1 , 2 and 3 , then the expression for () must factor as

rS

() = ( − 1 )( − 2 )( − 3 ). Multiplying these factors together gives us

() = [3 − (1 + 2 + 3 )2 + (1 2 + 1 3 + 2 3 ) − 1 2 3 ]

Equating the coefﬁcients of the 2 -terms for the two forms of gives us = −(1 + 2 + 3 ). Hence, the -coordinate of

−(1 + 2 + 3 )

1 + 2 + 3

=−

=

.

3

3

3

Fo

the point of inﬂection is −

65. By hypothesis = 0 is differentiable on an open interval containing . Since ( ()) is a point of inﬂection, the concavity

changes at = , so 00 () changes signs at = . Hence, by the First Derivative Test, 0 has a local extremum at = .

√

√

2 , we have that () = || = 2

N

67. Using the fact that || =

ot

Thus, by Fermat’s Theorem 00 () = 0.

⇒ 0 () =

√

√

√

2 + 2 = 2 2 = 2 || ⇒

−12

2

0 for 0 and 00 () 0 for 0, so (0 0) is an inﬂection point. But 00 (0) does not

=

00 () = 2 2

||

exist.

69. Suppose that is differentiable on an interval and 0 () 0 for all in except = . To show that is increasing on ,

let 1 , 2 be two numbers in with 1 2 .

Case 1 1 2 . Let be the interval { ∈ | }. By applying the Increasing/Decreasing Test to on , we see that is increasing on , so (1 ) (2 ).

Case 2 1 2 . Apply the Increasing/Decreasing Test to on = { ∈ | }.

Case 3 1 2 = . Apply the proof of the Increasing/Decreasing Test, using the Mean Value Theorem (MVT) on the interval [1 2 ] and noting that the MVT does not require to be differentiable at the endpoints of [1 2 ]. c ° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

SECTION 3.3

HOW DERIVATIVES AFFECT THE SHAPE OF A GRAPH

¤

127

Case 4 = 1 2 . Same proof as in Case 3.

Case 5 1 2 . By Cases 3 and 4, is increasing on [1 ] and on [ 2 ], so (1 ) () (2 ).

In all cases, we have shown that (1 ) (2 ). Since 1 , 2 were any numbers in with 1 2 , we have shown that is increasing on .

71. (a) () = 4 sin

1

⇒ 0 () = 4 cos

1

1

1

1

1

− 2 + sin (43 ) = 43 sin − 2 cos .

1

= 24 + () ⇒ 0 () = 83 + 0 ().

() = 4 2 + sin

1

= −24 + () ⇒ 0 () = −83 + 0 ().

() = 4 −2 + sin

1

4 sin − 0

() − (0)

1

= lim

= lim 3 sin . Since

It is given that (0) = 0, so (0) = lim

→0

→0

→0

−0

e

0

al

1

− 3 ≤ 3 sin ≤ 3 and lim 3 = 0, we see that 0 (0) = 0 by the Squeeze Theorem. Also,

→0

For 2 =

rS

0 (0) = 8(0)3 + 0 (0) = 0 and 0 (0) = −8(0)3 + 0 (0) = 0, so 0 is a critical number of , , and .

1

1

1

[ a nonzero integer], sin

= sin 2 = 0 and cos

= cos 2 = 1, so 0 (2 ) = −2 0.

2

2

2

2

1

1

1

, sin

= sin(2 + 1) = 0 and cos

= cos(2 + 1) = −1, so

(2 + 1)

2+1

2+1

Fo

For 2+1 =

0

0 (2+1 ) = 2

2+1 0. Thus, changes sign inﬁnitely often on both sides of 0.

Next, 0 (2 ) = 83 + 0 (2 ) = 83 − 2 = 2 (82 − 1) 0 for 2 1 , but

2

2

2

2

8

sides of 0.

ot

2

2

0

1

0 (2+1 ) = 83

2+1 + 2+1 = 2+1 (82+1 + 1) 0 for 2+1 − 8 , so changes sign inﬁnitely often on both

Last, 0 (2 ) = −83 + 0 (2 ) = −83 − 2 = −2 (82 + 1) 0 for 2 − 1 and

2

2

2

2

8

N

2

2

0

1

0 (2+1 ) = −83

2+1 + 2+1 = 2+1 (−82+1 + 1) 0 for 2+1 8 , so changes sign inﬁnitely often on both

sides of 0.

(b) (0) = 0 and since sin

1

1

and hence 4 sin is both positive and negative iniﬁnitely often on both sides of 0, and

arbitrarily close to 0, has neither a local maximum nor a local minimum at 0.

1

1

Since 2 + sin ≥ 1, () = 4 2 + sin

0 for 6= 0, so (0) = 0 is a local minimum.

1

1

0 for 6= 0, so (0) = 0 is a local maximum.

Since −2 + sin ≤ −1, () = 4 −2 + sin

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

128

¤

CHAPTER 3

APPLICATIONS OF DIFFERENTIATION

3.4 Limits at Infinity; Horizontal Asymptotes

1. (a) As becomes large, the values of () approach 5.

(b) As becomes large negative, the values of () approach 3.

3. (a) lim () = −2

(b) lim () = 2

→∞

(c) lim () = ∞

→−∞

→1

(e) Vertical: = 1, = 3; horizontal: = −2, = 2

(d) lim () = −∞

→3

5. If () = 22 , then a calculator gives (0) = 0, (1) = 05, (2) = 1, (3) = 1125, (4) = 1, (5) = 078125,

(6) = 05625, (7) = 03828125, (8) = 025, (9) = 0158203125, (10) = 009765625, (20) ≈ 000038147,

(50) ≈ 22204 × 10−12 , (100) ≈ 78886 × 10−27 .

It appears that lim 22 = 0.

→∞

=

[Limit Law 5]

lim (2 + 5 − 82 )

lim 3 − lim (1) + lim (42 )

→∞

→∞

→∞

lim 2 + lim (5) − lim (82 )

→∞

→∞

→∞

3 − lim (1) + 4 lim (12 )

→∞

3

2

[Theorem 5 of Section 1.8]

lim 3 − 2 lim 1

3 − 2

(3 − 2)

3 − 2

3 − 2(0)

3

→∞

→∞

= lim

= lim

=

=

=

2 + 1 →∞ (2 + 1) →∞ 2 + 1 lim 2 + lim 1

2+0

2

N

→∞

3 − 0 + 4(0)

2 + 5(0) − 8(0)

=

[Limit Laws 7 and 3]

→∞

ot

=

9. lim

→∞

2 + 5 lim (1) − 8 lim (12 )

→∞

[Limit Laws 1 and 2]

Fo

=

e

lim (3 − 1 + 42 )

→∞

→∞

=

al

→∞

[divide both the numerator and denominator by 2

(the highest power of that appears in the denominator)]

32 − + 4

(32 − + 4)2

= lim

2 + 5 − 8

→∞ (22 + 5 − 8)2

2

rS

7. lim

→∞

−2

( − 2)2

1 − 22

= lim

11. lim

= lim

=

→−∞ 2 + 1

→−∞ (2 + 1)2

→−∞ 1 + 12

→∞

lim 1 − 2 lim 12

→−∞

→−∞

lim 1 + lim 12

→−∞

→−∞

=

0 − 2(0)

=0

1+0

√

√

+ 2

( + 2 )2

132 + 1

0+1

13. lim

= lim

= lim

=

= −1

2

2 )2

→∞ 2 −

→∞ (2 −

→∞ 2 − 1

0−1

(22 + 1)2

(22 + 1)2 4

[(22 + 1)2 ]2

= lim

= lim

→∞ ( − 1)2 (2 + )

→∞ [( − 1)2 (2 + )]4

→∞ [(2 − 2 + 1)2 ][(2 + )2 ]

15. lim

(2 + 12 )2

(2 + 0)2

=

=4

2 )(1 + 1)

→∞ (1 − 2 + 1

(1 − 0 + 0)(1 + 0)

= lim

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

SECTION 3.4

√

√

96 −

96 − 3

=

= lim

3 +1

→∞

→∞ (3 + 1)3

17. lim

lim

=

→∞

lim 1 + lim (13 )

→∞

19. lim

→∞

9 − 15

(96 − )6 lim →∞

lim (1 +

→∞

=

→∞

[since 3 =

13 )

lim 9 − lim (15 )

→∞

→∞

1+0

LIMITS AT INFINITY; HORIZONTAL ASYMPTOTES

=

¤

129

√

6 for 0]

√

9−0 =3

√

2

√

√

92 + − 3

92 + + 3

92 + − (3)2

√

√

= lim

→∞

→∞

92 + + 3

92 + + 3

2

9 + − 92

1

= lim √

·

= lim √

→∞

→∞

92 + + 3

92 + + 3 1

√

92 + − 3 = lim

1

1

1

1

= lim

= lim

= √

=

=

→∞

3+3

6

9+3

92 2 + 2 + 3 →∞ 9 + 1 + 3

→∞

e

→∞

√

√

√

√

2 + − 2 +

2 + + 2 +

√

√

2 + + 2 +

al

√

√

21. lim

2 + − 2 + = lim

rS

(2 + ) − (2 + )

[( − )]

√

= lim √

= lim √

√

√

2 + +

2 +

2 + +

→∞

→∞

2 + 2

−

−

−

√

= √

=

= lim

→∞

2

1+0+ 1+0

1 + + 1 +

→∞

divide by the highest power of in the denominator

Fo

4 − 32 +

(4 − 32 + )3

= lim

→∞ (3 − + 2)3

3 − + 2

23. lim

− 3 + 12

=∞

→∞ 1 − 12 + 23

= lim

since the numerator increases without bound and the denominator approaches 1 as → ∞.

1

lim (4 + 5 ) = lim 5 ( + 1) [factor out the largest power of ] = −∞ because 5 → −∞ and 1 + 1 → 1

→−∞

→−∞

as → −∞.

Or:

lim

27. lim

→∞

4

+ 5 = lim 4 (1 + ) = −∞.

→−∞

N

→−∞

ot

25.

√ √

√

√

√

− 1 = ∞ since → ∞ and − 1 → ∞ as → ∞.

− = lim

29. If =

→∞

1 sin

1

1

, then lim sin = lim sin = lim

= 1.

→∞

→0+

→0+

31. (a)

(b)

()

−10,000

−04999625

−1,000,000

−04999996

−100,000

From the graph of () =

√

2 + + 1 + , we

−04999962

From the table, we estimate the limit to be −05.

estimate the value of lim () to be −05.

→−∞

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

130

¤

CHAPTER 3

APPLICATIONS OF DIFFERENTIATION

2

√ 2

√

√

+ + 1 − 2

++1−

2 + + 1 + = lim

2 + + 1 + √

= lim √

→−∞

→−∞

→−∞

2 + + 1 −

2 + + 1 −

(c) lim

( + 1)(1)

1 + (1)

= lim √

= lim

→−∞

2 + + 1 − (1) →−∞ − 1 + (1) + (12 ) − 1

1

1+0

√

=−

2

− 1+0+0−1

√

Note that for 0, we have 2 = || = −, so when we divide the radical by , with 0, we get

1 √ 2

1√ 2

+ + 1 = −√

+ + 1 = − 1 + (1) + (12 ).

2

1

1

1

2 + 1 lim 2 + lim 2 + lim

2+

2 + 1

→∞

→∞

= →∞

=

= lim

33. lim

= lim

2

2

→∞ − 2

→∞ − 2

→∞

2

1−

lim 1 − lim lim 1 −

→∞

→∞

→∞

=

2+0

= 2, so = 2 is a horizontal asymptote.

1−0

investigate = () =

2 + 1 as approaches 2.

−2

al

The denominator − 2 is zero when = 2 and the numerator is not zero, so we

e

=

lim () = −∞ because as

→2−

rS

→ 2− the numerator is positive and the denominator approaches 0 through

negative values. Similarly, lim () = ∞. Thus, = 2 is a vertical asymptote.

→2+

The graph conﬁrms our work.

22 + − 1

(2 − 1)( + 1)

=

, so lim () = ∞,

2 + − 2

( + 2)( − 1)

→−2−

N

= () =

ot

Fo

1

1

22 + − 1

1

1 lim 2 + − 2

2+ − 2

22 + − 1

2

= →∞

= lim

35. lim

= lim

2

1

2

→∞ 2 + − 2

→∞ + − 2

→∞

1

2

1+ − 2 lim 1 + − 2

→∞

2

1

1

− lim 2 lim 2 + lim

2+0−0

→∞

→∞

→∞

= 2, so = 2 is a horizontal asymptote.

=

=

1

1

1 + 0 − 2(0) lim 1 + lim

− 2 lim 2

→∞

→∞

→∞

lim () = −∞, lim () = −∞, and lim () = ∞. Thus, = −2

→1−

→−2+

→1+

and = 1 are vertical asymptotes. The graph conﬁrms our work.

37. = () =

2

(2 − 1)

( + 1)( − 1)

( + 1)

3 −

=

=

=

= () for 6= 1.

− 6 + 5

( − 1)( − 5)

( − 1)( − 5)

−5

The graph of is the same as the graph of with the exception of a hole in the graph of at = 1. By long division, () =

2 +

30

=+6+

.

−5

−5

As → ±∞, () → ±∞, so there is no horizontal asymptote. The denominator of is zero when = 5. lim () = −∞ and lim () = ∞, so = 5 is a

→5−

→5+

vertical asymptote. The graph conﬁrms our work. c ° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

SECTION 3.4

LIMITS AT INFINITY; HORIZONTAL ASYMPTOTES

¤

131

39. From the graph, it appears = 1 is a horizontal asymptote.

33 + 5002

3 + 500

3 + (500)

3

= lim 3 lim = lim

→∞ 3 + 5002 + 100 + 2000

→∞ + 5002 + 100 + 2000

→∞ 1 + (500) + (1002 ) + (20003 )

3

3+0

= 3, so = 3 is a horizontal asymptote.

=

1+0+0+0

3

2

The discrepancy can be explained by the choice of the viewing window. Try

[−100,000 100,000] by [−1 4] to get a graph that lends credibility to our calculation that = 3 is a horizontal asymptote.

lim () = 0 ⇒ degree of numerator degree of denominator

→±∞

al

(1)

e

41. Let’s look for a rational function.

(2) lim () = −∞ ⇒ there is a factor of 2 in the denominator (not just , since that would produce a sign

→0

rS

change at = 0), and the function is negative near = 0.

(3) lim () = ∞ and lim () = −∞ ⇒ vertical asymptote at = 3; there is a factor of ( − 3) in the

→3−

→3+

denominator.

Fo

(4) (2) = 0 ⇒ 2 is an -intercept; there is at least one factor of ( − 2) in the numerator.

Combining all of this information and putting in a negative sign to give us the desired left- and right-hand limits gives us

2−

as one possibility.

2 ( − 3)

ot

() =

43. (a) We must ﬁrst ﬁnd the function . Since has a vertical asymptote = 4 and -intercept = 1, − 4 is a factor of the

N

denominator and − 1 is a factor of the numerator. There is a removable discontinuity at = −1, so − (−1) = + 1 is a factor of both the numerator and denominator. Thus, now looks like this: () =

be determined. Then lim () = lim

→−1

= 5. Thus () =

(0) =

→−1

( − 1)( + 1)

, where is still to

( − 4)( + 1)

( − 1)( + 1)

( − 1)

(−1 − 1)

2

2

= lim

=

= , so = 2, and

→−1 − 4

( − 4)( + 1)

(−1 − 4)

5

5

5( − 1)( + 1) is a ratio of quadratic functions satisfying all the given conditions and

( − 4)( + 1)

5

5(−1)(1)

= .

(−4)(1)

4

2 − 1

(2 2 ) − (12 )

1−0

= 5 lim

=5

= 5(1) = 5

→∞ 2 − 3 − 4

→∞ (2 2 ) − (32 ) − (42 )

1−0−0

(b) lim () = 5 lim

→∞

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

132

¤

45. =

CHAPTER 3

APPLICATIONS OF DIFFERENTIATION

1− has domain (−∞ −1) ∪ (−1 ∞).

1+

lim

→±∞

1 − 1

1−

0−1

= lim

=

= −1, so = −1 is a HA.

1 + →±∞ 1 + 1

0+1

The line = −1 is a VA.

0 =

(1 + )(−1) − (1 − )(1)

−2

=

0 for 6= 1. Thus,

(1 + )2

(1 + )2

(−∞ −1) and (−1 ∞) are intervals of decrease.

00 = −2 ·

−2(1 + )

4

=

0 for −1 and 00 0 for −1, so the curve is CD on (−∞ −1) and CU on

(1 + )3

[(1 + )2 ]2

(−1 ∞). Since = −1 is not in the domain, there is no IP. lim →±∞

1

0

= lim

= 0, so = 0 is a

=

2 + 1 →±∞ 1 + 12

1+0

2 + 1 − (2)

1 − 2

= 2

= 0 when = ±1 and 0 0 ⇔

(2 + 1)2

( + 1)2

rS

0 =

al

horizontal asymptote.

e

47.

2 1 ⇔ −1 1, so is increasing on (−1 1) and decreasing on (−∞ −1) and (1 ∞).

√

√

(1 + 2 )2 (−2) − (1 − 2 )2(2 + 1)2

2(2 − 3)

=

0 ⇔ 3 or − 3 0, so is CU on

(1 + 2 )4

(1 + 2 )3

√

√

√

√

3 ∞ and − 3 0 and CD on −∞ − 3 and 0 3 .

Fo

00 =

The -intercept is

ot

49. = () = 4 − 6 = 4 (1 − 2 ) = 4 (1 + )(1 − ).

(0) = 0. The -intercepts are 0, −1, and 1 [found by solving () = 0 for ].

N

Since 4 0 for 6= 0, doesn’t change sign at = 0. The function does change sign at = −1 and = 1. As → ±∞, () = 4 (1 − 2 ) approaches −∞ because 4 → ∞ and (1 − 2 ) → −∞.

51. = () = (3 − )(1 + )2 (1 − )4 .

The -intercept is (0) = 3(1)2 (1)4 = 3.

The -intercepts are 3, −1, and 1. There is a sign change at 3, but not at −1 and 1.

When is large positive, 3 − is negative and the other factors are positive, so lim () = −∞. When is large negative, 3 − is positive, so

→∞

lim () = ∞.

→−∞

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

SECTION 3.4

LIMITS AT INFINITY; HORIZONTAL ASYMPTOTES

¤

133

53. First we plot the points which are known to be on the graph: (2 −1) and

(0 0). We can also draw a short line segment of slope 0 at = 2, since we are given that 0 (2) = 0. Now we know that 0 () 0 (that is, the function is decreasing) on (0 2), and that 00 () 0 on (0 1) and

00 () 0 on (1 2). So we must join the points (0 0) and (2 −1) in such a way that the curve is concave down on (0 1) and concave up on (1 2). The curve must be concave up and increasing on (2 4) and concave down and increasing toward = 1 on (4 ∞). Now we just need to reﬂect the curve in the -axis, since we are given that is an even function [the condition that (−) = () for all ].

55. We are given that (1) = 0 (1) = 0. So we can draw a short horizontal line at the point (1 0) to represent this situation. We

are given that = 0 and = 2 are vertical asymptotes, with lim () = −∞, lim () = ∞ and lim () = −∞, so

→0

→2−

e

we can draw the parts of the curve which approach these asymptotes.

→2+

al

On the interval (−∞ 0), the graph is concave down, and () → ∞ as

→ −∞. Between the asymptotes the graph is concave down. On the

rS

interval (2 ∞) the graph is concave up, and () → 0 as → ∞, so

= 0 is a horizontal asymptote. The diagram shows one possible function satisfying all of the given conditions.

sin

1

1

≤

≤ for 0. As → ∞, −1 → 0 and 1 → 0, so by the Squeeze

Fo

57. (a) Since −1 ≤ sin ≤ 1 for all −

Theorem, (sin ) → 0. Thus, lim

→∞

sin

= 0.

ot

(b) From part (a), the horizontal asymptote is = 0. The function

= (sin ) crosses the horizontal asymptote whenever sin = 0;

N

that is, at = for every integer . Thus, the graph crosses the asymptote an inﬁnite number of times.

59. (a) Divide the numerator and the denominator by the highest power of in ().

(a) If deg deg , then the numerator → 0 but the denominator doesn’t. So lim [ ()()] = 0.

→∞

(b) If deg deg , then the numerator → ±∞ but the denominator doesn’t, so lim [ ()()] = ±∞

→∞

(depending on the ratio of the leading coefﬁcients of and ).

61. lim

→∞

4 − 1

42 + 3

1

3

= lim 4 +

= lim 4 −

= 4 and lim

= 4. Therefore, by the Squeeze Theorem,

→∞

→∞

→∞

2

lim () = 4.

→∞

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

134

¤

CHAPTER 3

63. Let () =

32 + 1 and () = |() − 15|. Note that

22 + + 1

lim () =

→∞

APPLICATIONS OF DIFFERENTIATION

3

2

and lim () = 0. We are interested in ﬁnding the

→∞

-value at which () 005. From the graph, we ﬁnd that ≈ 14804, so we choose = 15 (or any larger number).

√

42 + 1

65. For = 05, we need to ﬁnd such that

− (−2) 05 ⇔

+1

√

42 + 1

−25

−15 whenever ≤ . We graph the three parts of this

+1

choose = −6 (or any smaller number).

√

42 + 1

−19 whenever ≤ From the

For = 01, we need −21

+1

al

graph, it seems that this inequality holds for ≤ −22. So we choose = −22

rS

(or any smaller number).

67. (a) 12 00001

e

inequality on the same screen, and see that the inequality holds for ≤ −6 So we

⇔ 2 100001 = 10 000 ⇔ 100 ( 0)

Fo

√

√

(b) If 0 is given, then 12 ⇔ 2 1 ⇔ 1 . Let = 1 .

1

1

1

1

⇒ 2 − 0 = 2 , so lim 2 = 0.

Then ⇒ √

→∞

69. For 0, |1 − 0| = −1. If 0 is given, then −1

⇒ −1 ⇒ |(1) − 0| = −1 , so lim (1) = 0.

→−∞

ot

Take = −1. Then

⇔ −1.

71. Suppose that lim () = . Then for every 0 there is a corresponding positive number such that | () − |

N

→∞

whenever . If = 1, then

⇔ 0 1 1

⇔

0 1. Thus, for every 0 there is a

corresponding 0 (namely 1) such that |(1) − | whenever 0 . This proves that lim (1) = = lim ().

→0+

→∞

Now suppose that lim () = . Then for every 0 there is a corresponding negative number such that

→−∞

| () − | whenever . If = 1, then

⇔ 1 1 0 ⇔ 1 0. Thus, for every

0 there is a corresponding 0 (namely −1) such that | (1) − | whenever − 0. This proves that lim (1) = = lim ().

→0−

→−∞

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

SECTION 3.5 SUMMARY OF CURVE SKETCHING

3.5 Summary of Curve Sketching

1. = () = 3 − 122 + 36 = (2 − 12 + 36) = ( − 6)2

A. is a polynomial, so = R.

B. -intercepts are 0 and 6, -intercept = (0) = 0 C. No symmetry D. No asymptote

E. 0 () = 32 − 24 + 36 = 3(2 − 8 + 12) = 3( − 2)( − 6) 0 ⇔

H.

2 6, so is decreasing on (2 6) and increasing on (−∞ 2) and (6 ∞).

F. Local maximum value (2) = 32, local minimum value (6) = 0

G. 00 () = 6 − 24 = 6( − 4) 0 ⇔ 4, so is CU on (4 ∞) and

CD on (−∞ 4). IP at (4 16)

3. = () = 4 − 4 = (3 − 4)

A. = R B. -intercepts are 0 and

√

3

4,

H.

e

-intercept = (0) = 0 C. No symmetry D. No asymptote

E. 0 () = 43 − 4 = 4(3 − 1) = 4( − 1)(2 + + 1) 0 ⇔ 1, so

al

is increasing on (1 ∞) and decreasing on (−∞ 1). F. Local minimum value

(1) = −3, no local maximum G. 00 () = 122 0 for all , so is CU on

5. = () = ( − 4)3

rS

(−∞ ∞). No IP

A. = R B. -intercepts are 0 and 4, -intercept (0) = 0 C. No symmetry

H.

Fo

D. No asymptote

E. () = · 3( − 4) + ( − 4) · 1 = ( − 4) [3 + ( − 4)]

0

2

3

2

= ( − 4)2 (4 − 4) = 4( − 1)( − 4)2 0

⇔

1, so is increasing on (1 ∞) and decreasing on (−∞ 1).

ot

F. Local minimum value (1) = −27, no local maximum value

G. 00 () = 4[( − 1) · 2( − 4) + ( − 4)2 · 1] = 4( − 4)[2( − 1) + ( − 4)]

= 4( − 4)(3 − 6) = 12( − 4)( − 2) 0

⇔

N

2 4, so is CD on (2 4) and CU on (−∞ 2) and (4 ∞). IPs at (2 −16) and (4 0)

7. = () =

1 5

5

− 8 3 + 16 = 1 4 − 8 2 + 16 A. = R B. -intercept 0, -intercept = (0) = 0

3

5

3

C. (−) = − (), so is odd; the curve is symmetric about the origin. D. No asymptote

E. 0 () = 4 − 82 + 16 = (2 − 4)2 = ( + 2)2 ( − 2)2 0 for all

H.

except ±2, so is increasing on R. F. There is no local maximum or minimum value.

G. 00 () = 43 − 16 = 4(2 − 4) = 4( + 2)( − 2) 0 ⇔

−2 0 or 2, so is CU on (−2 0) and (2 ∞), and is CD on

(−∞ −2) and (0 2). IP at −2 − 256 , (0 0), and 2 256

15

15

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

¤

135

136

¤

CHAPTER 3

APPLICATIONS OF DIFFERENTIATION

A. = { | 6= 1} = (−∞ 1) ∪ (1 ∞) B. -intercept = 0, -intercept = (0) = 0

= 1, so = 1 is a HA. lim

= −∞, lim

= ∞, so = 1 is a VA.

C. No symmetry D. lim

→±∞ − 1

→1− − 1

→1+ − 1

9. = () = ( − 1)

E. 0 () =

( − 1) −

−1

=

0 for 6= 1, so is

( − 1)2

( − 1)2

H.

decreasing on (−∞ 1) and (1 ∞) F. No extreme values

G. 00 () =

2

0 ⇔ 1, so is CU on (1 ∞) and

( − 1)3

CD on (−∞ 1). No IP

11. = () =

− 2

(1 − )

=

=

for 6= 1. There is a hole in the graph at (1 1).

2 − 3 + 2

(1 − )(2 − )

2−

(2 − )(1) − (−1)

2

=

0 [ 6= 1 2], so is

(2 − )2

(2 − )2

G. 0 () = 2(2 − )−2

⇒

00 () = −4(2 − )−3 (−1) =

H.

rS

increasing on (−∞ 1), (1 2), and (2 ∞). F. No extrema

al

E. 0 () =

e

A. = { | 6= 1 2} = (−∞ 1) ∪ (1 2) ∪ (2 ∞) B. -intercept = 0, -intercept = (0) = 0 C. No symmetry

= −1, so = −1 is a HA. lim

= ∞, lim

= −∞, so = 2 is a VA.

D. lim

→±∞ 2 −

→2− 2 −

→2+ 2 −

4

0 ⇔ 2, so is CU on

(2 − )3

Fo

(−∞ 1) and (1 2), and is CD on (2 ∞). No IP

A. = { | 6= ±3} = (−∞ −3) ∪ (−3 3) ∪ (3 ∞) B. -intercept = (0) = − 1 , no

9

13. = () = 1(2 − 9)

-intercept C. (−) = () ⇒ is even; the curve is symmetric about the -axis. D.

→3−

1

1

1

1

= −∞, lim 2

= ∞, lim

= ∞, lim

= −∞, so = 3 and = −3

2

2

2 − 9

→3+ − 9

→−3− − 9

→−3+ − 9

2

0 ⇔ 0 ( 6= −3) so is increasing on (−∞ −3) and (−3 0) and

(2 − 9)2

N

are VA. E. 0 () = −

decreasing on (0 3) and (3 ∞). F. Local maximum value (0) = − 1 .

9

G. 00 =

1

= 0, so = 0

2 − 9

ot

is a HA. lim

lim

→±∞

H.

−2(2 − 9)2 + (2)2(2 − 9)(2)

6(2 + 3)

= 2

0 ⇔

2 − 9)4

(

( − 9)3

2 9 ⇔ 3 or −3, so is CU on (−∞ −3) and (3 ∞) and

CD on (−3 3). No IP

15. = () = (2 + 9)

A. = R B. -intercept: (0) = 0; -intercept: () = 0 ⇔ = 0

C. (−) = − (), so is odd and the curve is symmetric about the origin. D.

HA; no VA E. 0 () =

lim [(2 + 9)] = 0, so = 0 is a

→±∞

(2 + 9)(1) − (2)

9 − 2

(3 + )(3 − )

= 2

=

0 ⇔ −3 3, so is increasing

2 + 9)2

(

( + 9)2

(2 + 9)2

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

SECTION 3.5 SUMMARY OF CURVE SKETCHING

¤

137

on (−3 3) and decreasing on (−∞ −3) and (3 ∞). F. Local minimum value (−3) = − 1 , local maximum

6

value (3) =

1

6

(2)(2 + 9) −(2 + 9) − 2(9 − 2 )

(2 + 9)2 (−2) − (9 − 2 ) · 2(2 + 9)(2)

=

[(2 + 9)2 ]2

(2 + 9)4

√

√

2(2 − 27)

=

= 0 ⇔ = 0, ± 27 = ±3 3

H.

(2 + 9)3

√

√

√

00 () 0 ⇔ −3 3 0 or 3 3, so is CU on −3 3 0

√

√

√ and 3 3 ∞ , and CD on −∞ −3 3 and 0 3 3 . There are three

√

√

1

inﬂection points: (0 0) and ±3 3 ± 12 3 .

G. 00 () =

−1

2

A. = { | 6= 0} = (−∞ 0) ∪ (0 ∞) B. No -intercept; -intercept: () = 0 ⇔ = 1

C. No symmetry D.

−1

−1

= 0, so = 0 is a HA. lim

= −∞, so = 0 is a VA.

→0 2

2

2 · 1 − ( − 1) · 2

−( − 2)

−2 + 2

=

=

, so 0 () 0 ⇔ 0 2 and 0 () 0 ⇔

(2 )2

4

3

al

E. 0 () =

lim

→±∞

e

17. = () =

0 or 2. Thus, is increasing on (0 2) and decreasing on (−∞ 0)

H.

rS

and (2 ∞). F. No local minimum, local maximum value (2) = 1 .

4

3 · (−1) − [−( − 2)] · 32

23 − 62

2( − 3)

=

=

.

3 )2

(

6

4

G. 00 () =

19. = () =

Fo

00 () is negative on (−∞ 0) and (0 3) and positive on (3 ∞), so is CD

on (−∞ 0) and (0 3) and CU on (3 ∞). IP at 3 2

9

(2 + 3) − 3

3

2

=

=1− 2

+3

2 + 3

+3

2

A. = R B. -intercept: (0) = 0;

D.

ot

-intercepts: () = 0 ⇔ = 0 C. (−) = (), so is even; the graph is symmetric about the -axis.

−2

6

2

= 2

.

= 1, so = 1 is a HA. No VA. E. Using the Reciprocal Rule, 0 () = −3 · 2

+3

( + 3)2

( + 3)2

lim

→±∞ 2

N

0 () 0 ⇔ 0 and 0 () 0 ⇔ 0, so is decreasing on (−∞ 0) and increasing on (0 ∞).

F. Local minimum value (0) = 0, no local maximum.

G. 00 () =

=

(2 + 3)2 · 6 − 6 · 2(2 + 3) · 2

[(2 + 3)2 ]2

H.

6(2 + 3)[(2 + 3) − 42 ]

6(3 − 32 )

−18( + 1)( − 1)

=

=

2 + 3)4

(

(2 + 3)3

(2 + 3)3

00 () is negative on (−∞ −1) and (1 ∞) and positive on (−1 1),

so is CD on (−∞ −1) and (1 ∞) and CU on (−1 1). IP at ±1 1

4

√

21. = () = ( − 3) = 32 − 312

A. = [0 ∞) B. -intercepts: 0 3; -intercept = (0) = 0 C. No

symmetry D. No asymptote E. 0 () = 3 12 − 3 −12 = 3 −12 ( − 1) =

2

2

2

3( − 1)

√

0

2

⇔

1,

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

138

¤

CHAPTER 3

APPLICATIONS OF DIFFERENTIATION

H.

so is increasing on (1 ∞) and decreasing on (0 1).

F. Local minimum value (1) = −2, no local maximum value

G. 00 () = 3 −12 + 3 −32 = 3 −32 ( + 1) =

4

4

4

3( + 1)

0 for 0,

432

so is CU on (0 ∞). No IP

23. = () =

√

2 + − 2 = ( + 2)( − 1) A. = { | ( + 2)( − 1) ≥ 0} = (−∞ −2] ∪ [1 ∞)

B. -intercept: none; -intercepts: −2 and 1 C. No symmetry D. No asymptote

E. 0 () = 1 (2 + − 2)−12 (2 + 1) =

2

2

2 + 1

√

, 0 () = 0 if = − 1 , but − 1 is not in the domain.

2

2

2 + − 2

0 () 0 ⇒ − 1 and 0 () 0 ⇒ − 1 , so (considering the domain) is increasing on (1 ∞) and

2

2

is decreasing on (−∞ −2). F. No local extrema

2(2 + − 2)12 (2) − (2 + 1) · 2 · 1 (2 + − 2)−12 (2 + 1)

2

√

2

2 2 + − 2

(2 + − 2)−12 4(2 + − 2) − (42 + 4 + 1)

=

4(2 + − 2)

al

−9

0

4(2 + − 2)32

so is CD on (−∞ −2) and (1 ∞). No IP

A. = R B. -intercept: (0) = 0; -intercepts: () = 0 ⇒ = 0

Fo

√

25. = () = 2 + 1

rS

=

H.

e

G. 00 () =

C. (−) = − (), so is odd; the graph is symmetric about the origin.

1

1

√ = lim

=1

= √

D. lim () = lim √

= lim √

= lim √

→∞

→∞

→∞

1+0

2 + 1 →∞ 2 + 1 →∞ 2 + 1 2

1 + 12

ot

and

1

√ = lim

= lim √

= lim √ lim () = lim √

→−∞

→−∞ −

2 + 1 →−∞ 2 + 1 →−∞ 2 + 1 − 2

1 + 12

→−∞

No VA.

0

E. () =

1

√

= −1 so = ±1 are HA.

− 1+0

N

=

√

2 + 1 − ·

2

√

2 + 1 − 2

1

2 + 1

=

=

0 for all , so is increasing on R.

2 + 1)12 ]2

[(

(2 + 1)32

(2 + 1)32

2

H.

F. No extreme values

G. 00 () = − 3 (2 + 1)−52 · 2 =

2

−3

, so 00 () 0 for 0

(2 + 1)52

and 00 () 0 for 0. Thus, is CU on (−∞ 0) and CD on (0 ∞).

IP at (0 0)

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

SECTION 3.5 SUMMARY OF CURVE SKETCHING

¤

√

1 − 2 A. = { | || ≤ 1, 6= 0} = [−1 0) ∪ (0 1] B. -intercepts ±1, no -intercept

√

√

1 − 2

1 − 2

C. (−) = − (), so the curve is symmetric about (0 0) D. lim

= ∞, lim

= −∞,

+

−

→0

→0

√

2√

− 1 − 2 − 1 − 2

1

0 so = 0 is a VA. E. () =

=− √

0, so is decreasing

2

2

1 − 2

27. = () =

H.

on (−1 0) and (0 1). F. No extreme values

G. 00 () =

2 − 32

2 )32

0 ⇔ −1 − 2 or 0 2 , so

3

3

3 (1 −

2

1 .

is CU on −1 − 2 and 0 2 and CD on − 2 0 and

3

3

3

3

1

IP at ± 2 ± √2

3

A. = R B. -intercept: (0) = 0; -intercepts: () = 0 ⇒ = 313 ⇒

√

3 = 27 ⇒ 3 − 27 = 0 ⇒ (2 − 27) = 0 ⇒ = 0, ±3 3 C. (−) = − (), so is odd;

al

e

29. = () = − 313

rS

the graph is symmetric about the origin. D. No asymptote E. 0 () = 1 − −23 = 1 −

1

23

=

23 − 1

.

23

0 () 0 when || 1 and 0 () 0 when 0 || 1, so is increasing on (−∞ −1) and (1 ∞), and decreasing on (−1 0) and (0 1) [hence decreasing on (−1 1) since is

H.

continuous on (−1 1)]. F. Local maximum value (−1) = 2, local minimum

Fo

value (1) = −2 G. 00 () = 2 −53 0 when 0 and 00 () 0

3

when 0, so is CD on (−∞ 0) and CU on (0 ∞). IP at (0 0)

31. = () =

√

3

2 − 1 A. = R B. -intercept: (0) = −1; -intercepts: () = 0 ⇔ 2 − 1 = 0 ⇔

ot

= ±1 C. (−) = (), so the curve is symmetric about the -axis D. No asymptote

N

E. 0 () = 1 (2 − 1)−23 (2) =

3

2

. 0 () 0 ⇔ 0 and 0 () 0 ⇔ 0, so is

3

3 (2 − 1)2

increasing on (0 ∞) and decreasing on (−∞ 0). F. Local minimum value (0) = −1

G. 00 () =

=

2

23

2

−13

(2)

2 ( − 1) (1) − · 2 ( − 1)

3

·

3

[(2 − 1)23 ]2

H.

2 (2 − 1)−13 [3(2 − 1) − 42 ]

2(2 + 3)

·

=−

2 − 1)43

9

(

9(2 − 1)53

00 () 0 ⇔ −1 1 and 00 () 0 ⇔ −1 or 1, so

is CU on (−1 1) and is CD on (−∞ −1) and (1 ∞). IP at (±1 0)

33. = () = sin3

A. = R B. -intercepts: () = 0 ⇔ = , an integer; -intercept = (0) = 0

C. (−) = − (), so is odd and the curve is symmetric about the origin. Also, ( + 2) = (), so is periodic with period 2, and we determine E–G for 0 ≤ ≤ . Since is odd, we can reﬂect the graph of on [0 ] about the

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

139

¤

140

CHAPTER 3

APPLICATIONS OF DIFFERENTIATION

origin to obtain the graph of on [− ], and then since has period 2, we can extend the graph of for all real numbers.

D. No asymptote E. 0 () = 3 sin2 cos 0 ⇔ cos 0 and sin 6= 0 ⇔ 0 , so is increasing on

2

0 2 and is decreasing on 2 . F. Local maximum value 2 = 1 local minimum value − = −1

2

G. 00 () = 3 sin2 (− sin ) + 3 cos (2 sin cos ) = 3 sin (2 cos2 − sin2 )

= 3 sin [2(1 − sin2 ) − sin2 ] = 3 sin (2 − 3 sin2 ) 0 ⇔

sin 0 and sin2 2 ⇔ 0 and 0 sin 2 ⇔ 0 sin−1 2 let = sin−1 2 or

3

3

3

3

− , so is CU on (0 ) and ( − ), and is CD on ( − ). There are inﬂection points at = 0, , ,

and = − .

35. = () = tan , −

2

symmetric about the -axis. D.

rS

al

e

H.

B. Intercepts are 0 C. (−) = (), so the curve is

A. = −

2 2

2

lim

→(2)−

tan = ∞ and

lim

→−(2)+

tan = ∞, so =

Fo

E. 0 () = tan + sec2 0 ⇔ 0 , so increases on 0

2

2

and decreases on − 0 . F. Absolute and local minimum value (0) = 0.

2

1

2

H.

so is

− sin , 0 3

A. = (0 3) B. No -intercept. The -intercept, approximately 19, can be

N

37. = () =

,

2

and = − are VA.

2

ot

G. 00 = 2 sec2 + 2 tan sec2 0 for −

2

CU on − 2 2 . No IP

2

found using Newton’s Method. C. No symmetry D. No asymptote E. 0 () = 1 − cos 0 ⇔ cos

2

7

5

5

7

and 3 3 and decreasing on 0 and 5 7 .

3 3 or 3 3, so is increasing on 3 3

3

3

3

F. Local minimum value

5

3

=

5

6

+

√

3

,

2

3

=

6

−

√

3

,

2

local minimum value

local maximum value

7

3

=

7

6

−

39. = () =

sin

1 + cos

when

cos 6= 1

=

⇔

H.

√

3

2

G. 00 () = sin 0 ⇔ 0 or 2 3, so is CU on

(0 ) and (2 3) and CD on ( 2). IPs at and (2 )

2

1

2

1 − cos sin (1 − cos ) sin

1 − cos

·

=

= csc − cot

=

1 + cos 1 − cos sin sin2

A. The domain of is the set of all real numbers except odd integer multiples of ; that is, all reals except (2 + 1), where c ° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

SECTION 3.5 SUMMARY OF CURVE SKETCHING

¤

141

is an integer. B. -intercept: (0) = 0; -intercepts: = 2, an integer. C. (−) = − (), so is an odd function; the graph is symmetric about the origin and has period 2. D. When is an odd integer, lim →()−

() = ∞ and

E. 0 () =

lim

→()+

() = −∞, so = is a VA for each odd integer . No HA.

(1 + cos ) · cos − sin (− sin )

1 + cos

1

=

=

. 0 () 0 for all except odd multiples of

(1 + cos )2

(1 + cos )2

1 + cos

, so is increasing on ((2 − 1) (2 + 1)) for each integer . F. No extreme values

G. 00 () =

sin

0 ⇒ sin 0 ⇒

(1 + cos )2

H.

∈ (2 (2 + 1)) and 00 () 0 on ((2 − 1) 2) for each integer . is CU on (2 (2 + 1)) and CD on ((2 − 1) 2)

e

for each integer . has IPs at (2 0) for each integer .

al

0

. The m-intercept is (0) = 0 . There are no -intercepts. lim () = ∞, so = is a VA.

→−

1 − 2 2

41. = () =

0

0

0

= 2 2

= 2

0, so is

2 32

2 (1 − 2 2 )32

( − 2 )32

( − )

3

increasing on (0 ). There are no local extreme values.

=

(2 − 2 )32 (0 ) − 0 · 3 (2 − 2 )12 (−2)

2

[(2 − 2 )32 ]2

Fo

00 () =

rS

0 () = − 1 0 (1 − 2 2 )−32 (−22 ) =

2

0 (2 − 2 )12 [(2 − 2 ) + 3 2 ]

0 (2 + 2 2 )

=

0,

2 − 2 )3

(

(2 − 2 )52

43. = −

4

3 2 2

2 2

+

−

=−

− 2 + 2

24

12

24

24

− 2

( − )2 = 2 ( − )2

24

N

=

ot

so is CU on (0 ). There are no inﬂection points.

where = −

is a negative constant and 0 ≤ ≤ . We sketch

24

() = 2 ( − )2 for = −1. (0) = () = 0.

0 () = 2 [2( − )] + ( − )2 (2) = 2( − )[ + ( − )] = 2( − )(2 − ). So for 0 ,

0 () 0 ⇔ ( − )(2 − ) 0 [since 0] ⇔ 2 and 0 () 0 ⇔ 0 2.

Thus, is increasing on (2 ) and decreasing on (0 2), and there is a local and absolute

minimum at the point (2 (2)) = 2 4 16 . 0 () = 2[( − )(2 − )] ⇒

00 () = 2[1( − )(2 − ) + (1)(2 − ) + ( − )(2)] = 2(62 − 6 + 2 ) = 0 ⇔

√

√

6 ± 122

= 1 ± 63 , and these are the -coordinates of the two inﬂection points.

=

2

12

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

142

¤

45. =

CHAPTER 3

APPLICATIONS OF DIFFERENTIATION

2 + 1

. Long division gives us:

+1

−1

2

+1

+1

2 +

−+1

−−1

2

2

2

2 + 1

=−1+

and () − ( − 1) =

=

Thus, = () =

+1

+1

+1

2

1+

[for 6= 0] → 0 as → ±∞.

1

So the line = − 1 is a slant asymptote (SA).

47. =

43 − 22 + 5

. Long division gives us:

22 + − 3

22 + − 3 43 − 22

2 − 2

+5

e

43 + 22 − 6

al

− 42 + 6 + 5

− 42 − 2 + 6

rS

8 − 1

8 − 1

8 − 1

43 − 22 + 5

= 2 − 2 + 2 and () − (2 − 2) = 2

=

Thus, = () =

22 + − 3

2 + − 3

2 + − 3

8

1

− 2

1

3

2+ − 2

49. = () =

1

2

=+1+

−1

−1

Fo

[for 6= 0] → 0 as → ±∞. So the line = 2 − 2 is a SA.

A. = (−∞ 1) ∪ (1 ∞) B. -intercept: () = 0 ⇔ = 0;

-intercept: (0) = 0 C. No symmetry D. lim () = −∞ and lim () = ∞, so = 1 is a VA.

→1−

→±∞

→±∞

1

( − 1)2 − 1

2 − 2

( − 2)

=

=

=

0 for

2

2

( − 1)

( − 1)

( − 1)2

( − 1)2

H.

N

E. 0 () = 1 −

1

= 0, so the line = + 1 is a SA.

−1

ot

lim [ () − ( + 1)] = lim

→1+

0 or 2, so is increasing on (−∞ 0) and (2 ∞), and is decreasing on (0 1) and (1 2). F. Local maximum value (0) = 0, local minimum value

(2) = 4 G. 00 () =

2

0 for 1, so is CU on (1 ∞) and

( − 1)3

is CD on (−∞ 1). No IP

51. = () =

3 + 4

4

=+ 2

2

√

A. = (−∞ 0) ∪ (0 ∞) B. -intercept: () = 0 ⇔ = − 3 4; no -intercept

C. No symmetry D. lim () = ∞, so = 0 is a VA.

→0

lim [ () − ] = lim

→±∞

→±∞

4

= 0, so = is a SA.

2

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

SECTION 3.5 SUMMARY OF CURVE SKETCHING

E. 0 () = 1 −

8

3 − 8

=

0 for 0 or 2, so is increasing on

3

3

¤

143

H.

(−∞ 0) and (2 ∞), and is decreasing on (0 2). F. Local minimum value

(2) = 3, no local maximum value G. 00 () =

24

0 for 6= 0, so is CU

4

on (−∞ 0) and (0 ∞). No IP

53. = () =

−2

23 + 2 + 1

= 2 + 1 + 2

2 + 1

+1

A. = R B. -intercept: (0) = 1; -intercept: () = 0 ⇒

0 = 23 + 2 + 1 = ( + 1)(22 − + 1) ⇒ = −1 C. No symmetry D. No VA lim [ () − (2 + 1)] = lim

→±∞

→±∞

(2 + 1)(−2) − (−2)(2)

2(4 + 22 + 1) − 22 − 2 + 42

24 + 62

22 (2 + 3)

=

=

=

2 + 1)2

2 + 1)2

2 + 1)2

(

(

(

(2 + 1)2

e

E. 0 () = 2 +

−2

−2

= lim

= 0, so the line = 2 + 1 is a slant asymptote.

2 + 1 →±∞ 1 + 12

so 0 () 0 if 6= 0. Thus, is increasing on (−∞ 0) and (0 ∞). Since is continuous at 0, is increasing on R.

(2 + 1)2 · (83 + 12) − (24 + 62 ) · 2(2 + 1)(2)

[(2 + 1)2 ]2

rS

G. 00 () =

al

F. No extreme values

4(2 + 1)[(2 + 1)(22 + 3) − 24 − 62 ]

4(−2 + 3)

=

(2 + 1)4

(2 + 1)3

√

√ so 00 () 0 for − 3 and 0 3, and 00 () 0 for

H.

√

√

√

√

− 3 0 and 3. is CU on −∞ − 3 and 0 3 ,

√

√

and CD on − 3 0 and

3 ∞ . There are three IPs: (0 1),

√

√

− 3 − 3 3 + 1 ≈ (−173 −160), and

2

√ 3 √

3 2 3 + 1 ≈ (173 360).

ot

Fo

=

√

4

42 + 9 ⇒ 0 () = √

⇒

42 + 9

√

√

42 + 9 · 4 − 4 · 4 42 + 9

4(42 + 9) − 162

36

=

. is deﬁned on (−∞ ∞).

00 () =

=

2 +9

4

(42 + 9)32

(42 + 9)32

N

55. = () =

(−) = (), so is even, which means its graph is symmetric about the -axis. The -intercept is (0) = 3. There are no

-intercepts since () 0 for all

√

√

√

42 + 9 − 2

42 + 9 + 2

2 + 9 − 2 = lim

√

4 lim →∞

→∞

42 + 9 + 2

(42 + 9) − 42

9

= lim √

=0

= lim √

→∞

→∞

42 + 9 + 2

42 + 9 + 2

and, similarly, lim

→−∞

√

9

42 + 9 + 2 = lim √

= 0,

→−∞

42 + 9 − 2

so = ±2 are slant asymptotes. is decreasing on (−∞ 0) and increasing on (0 ∞) with local minimum (0) = 3.

00 () 0 for all , so is CU on R.

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

144

57.

¤

CHAPTER 3

APPLICATIONS OF DIFFERENTIATION

2

2

√ 2

− 2 =1 ⇒ =±

− 2 . Now

2

√

√

2 − 2 +

−2

√ 2

2 −

2 − 2 − √

= · lim

−

= · lim √

= 0, lim →∞

→∞

→∞ 2 − 2 +

2 − 2 +

is a slant asymptote. Similarly,

−2

√ 2

2 − − lim −

= − · lim √

−

= 0, so = − is a slant asymptote.

→∞

→∞ 2 − 2 +

which shows that =

4 + 1

1

4

() − 3 = lim

−

= lim

= 0, so the graph of is asymptotic to that of = 3

→±∞

→±∞

→±∞

1

= −∞ and

A. = { | 6= 0} B. No intercept C. is symmetric about the origin. D. lim 3 +

→0−

1

lim 3 +

= ∞, so = 0 is a vertical asymptote, and as shown above, the graph of is asymptotic to that of = 3 .

→0+

1

1

1

E. 0 () = 32 − 12 0 ⇔ 4 1 ⇔ || √3 , so is increasing on −∞ − √ and √ ∞ and

4

3

4

4

3

3

1

1

H.

decreasing on − √ 0 and 0 √ . F. Local maximum value

4

4

3

3

1

1

−54

−√

, local minimum value √

= −4 · 3

= 4 · 3−54

4

4

3

3 lim rS

al

e

59.

on (−∞ 0). No IP

Fo

G. 00 () = 6 + 23 0 ⇔ 0, so is CU on (0 ∞) and CD

ot

3.6 Graphing with Calculus and Calculators

1. () = 44 − 323 + 892 − 95 + 29

⇒ 0 () = 163 − 962 + 178 − 95 ⇒ 00 () = 482 − 192 + 178.

N

() = 0 ⇔ ≈ 05, 160; 0 () = 0 ⇔ ≈ 092, 25, 258 and 00 () = 0

⇔

≈ 146, 254.

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

SECTION 3.6

GRAPHING WITH CALCULUS AND CALCULATORS

¤

145

From the graphs of 0 , we estimate that 0 0 and that is decreasing on (−∞ 092) and (25 258), and that 0 0 and is increasing on (092 25) and (258 ∞) with local minimum values (092) ≈ −512 and (258) ≈ 3998 and local maximum value (25) = 4. The graphs of 0 make it clear that has a maximum and a minimum near = 25, shown more clearly in the fourth graph.

From the graph of 00 , we estimate that 00 0 and that is CU on

(−∞ 146) and (254 ∞), and that 00 0 and is CD on (146 254).

There are inﬂection points at about (146 −140) and (254 3999).

3. () = 6 − 105 − 4004 + 25003

00

4

3

⇒ 0 () = 65 − 504 − 16003 + 75002

⇒

2

ot

Fo

rS

al

e

() = 30 − 200 − 4800 + 1500

From the graph of 0 , we estimate that is decreasing on (−∞ −15), increasing on (−15 440), decreasing

N

on (440 1893), and increasing on (1893 ∞), with local minimum values of (−15) ≈ −9,700,000 and

(18.93) ≈ −12,700,000 and local maximum value (440) ≈ 53,800. From the graph of 00 , we estimate that is CU on

(−∞ −1134), CD on (−1134 0), CU on (0 292), CD on (292 1508), and CU on (1508 ∞). There is an inﬂection point at (0 0) and at about (−1134 −6,250,000), (292 31,800), and (1508 −8,150,000).

5. () =

3 + 2 + 1

⇒ 0 () = −

23 + 2 − 1

(3 + 2 + 1)2

⇒ 00 () =

2(34 + 33 + 2 − 6 − 3)

(3 + 2 + 1)3

[continued]

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

146

¤

CHAPTER 3

APPLICATIONS OF DIFFERENTIATION

From the graph of , we see that there is a VA at ≈ −147. From the graph of 0 , we estimate that is increasing on

(−∞ −147), increasing on (−147 066), and decreasing on (066 ∞), with local maximum value (066) ≈ 038.

From the graph of 00 , we estimate that is CU on (−∞ −147), CD on (−147 −049), CU on (−049 0), CD on

(0 110), and CU on (110 ∞). There is an inﬂection point at (0 0) and at about (−049 −044) and (110 031).

7. () = 6 sin + cot , − ≤ ≤

⇒ 0 () = 6 cos − csc2 ⇒ 00 () = −6 sin + 2 csc2 cot

e

From the graph of , we see that there are VAs at = 0 and = ±. is an odd function, so its graph is symmetric about the origin. From the graph of 0 , we estimate that is decreasing on (− −140), increasing on (−140 −044), decreasing

al

on (−044 0), decreasing on (0 044), increasing on (044 140), and decreasing on (140 ), with local minimum values

(−140) ≈ −609 and (044) ≈ 468, and local maximum values (−044) ≈ −468 and (140) ≈ 609.

rS

From the graph of 00 , we estimate that is CU on (− −077), CD on (−077 0), CU on (0 077), and CD on

(077 ). There are IPs at about (−077 −522) and (077 522).

⇒ 0 () = −

1

16

3

1

− 3 − 4 = − 4 (2 + 16 + 3) ⇒

2

2

48

12

2

+ 4 + 5 = 5 (2 + 24 + 6).

3

N

ot

00 () =

8

1

1

+ 2 + 3

Fo

9. () = 1 +

From the graphs, it appears that increases on (−158 −02) and decreases on (−∞ −158), (−02 0), and (0 ∞); that has a local minimum value of (−158) ≈ 097 and a local maximum value of (−02) ≈ 72; that is CD on (−∞ −24) and (−025 0) and is CU on (−24 −025) and (0 ∞); and that has IPs at (−24 097) and (−025 60).

√

√

−16 ± 256 − 12

To ﬁnd the exact values, note that 0 = 0 ⇒ =

= −8 ± 61 [≈ −019 and −1581].

2

√

√

√

0 is positive ( is increasing) on −8 − 61 −8 + 61 and 0 is negative ( is decreasing) on −∞ −8 − 61 ,

√

√

√

−24 ± 576 − 24

−8 + 61 0 , and (0 ∞). 00 = 0 ⇒ =

= −12 ± 138 [≈ −025 and −2375]. 00 is

2

√

√

√

positive ( is CU) on −12 − 138 −12 + 138 and (0 ∞) and 00 is negative ( is CD) on −∞ −12 − 138

√

and −12 + 138 0 . c ° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

SECTION 3.6

11.

() =

GRAPHING WITH CALCULUS AND CALCULATORS

¤

147

( + 4)( − 3)2 has VA at = 0 and at = 1 since lim () = −∞,

→0

4 ( − 1)

lim () = −∞ and lim () = ∞.

→1−

→1+

+ 4 ( − 3)2

·

(1 + 4)(1 − 3)2 dividing numerator

2

→0

() =

=

3

4

and denominator by

( − 1)

· ( − 1)

3

as → ±∞, so is asymptotic to the -axis.

Since is undeﬁned at = 0, it has no -intercept. () = 0 ⇒ ( + 4)( − 3)2 = 0 ⇒ = −4 or = 3, so has

-intercepts −4 and 3. Note, however, that the graph of is only tangent to the -axis and does not cross it at = 3, since is

rS

al

e

positive as → 3− and as → 3+ .

From these graphs, it appears that has three maximum values and one minimum value. The maximum values are approximately (−56) = 00182, (082) = −2815 and (52) = 00145 and we know (since the graph is tangent to the

2 ( + 1)3

( − 2)2 ( − 4)4

⇒ 0 () = −

( + 1)2 (3 + 182 − 44 − 16)

( − 2)3 ( − 4)5

[from CAS].

N

ot

13. () =

Fo

-axis at = 3) that the minimum value is (3) = 0.

From the graphs of 0 , it seems that the critical points which indicate extrema occur at ≈ −20, −03, and 25, as estimated in Example 3. (There is another critical point at = −1, but the sign of 0 does not change there.) We differentiate again, obtaining 00 () = 2

( + 1)(6 + 365 + 64 − 6283 + 6842 + 672 + 64)

.

( − 2)4 ( − 4)6

[continued] c ° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

148

¤

CHAPTER 3

APPLICATIONS OF DIFFERENTIATION

From the graphs of 00 , it appears that is CU on (−353 −50), (−1 −05), (−01 2), (2 4) and (4 ∞) and CD on (−∞ −353), (−50 −1) and (−05 −01). We check back on the graphs of to ﬁnd the -coordinates of the inﬂection points, and ﬁnd that these points are approximately (−353 −0015), (−50 −0005), (−1 0), (−05 000001), and (−01 00000066).

15. () =

3 + 52 + 1

−(5 + 104 + 63 + 42 − 3 − 22)

. From a CAS, 0 () = and 4 + 3 − 2 + 2

(4 + 3 − 2 + 2)2

2(9 + 158 + 187 + 216 − 95 − 1354 − 763 + 212 + 6 + 22)

(4 + 3 − 2 + 2)3

al

e

00 () =

rS

The ﬁrst graph of shows that = 0 is a HA. As → ∞, () → 0 through positive values. As → −∞, it is not clear if

() → 0 through positive or negative values. The second graph of shows that has an -intercept near −5, and will have a

ot

Fo

local minimum and inﬂection point to the left of −5.

From the two graphs of 0 , we see that 0 has four zeros. We conclude that is decreasing on (−∞ −941), increasing on

N

(−941 −129), decreasing on (−129 0), increasing on (0 105), and decreasing on (105 ∞). We have local minimum values (−941) ≈ −0056 and (0) = 05, and local maximum values (−129) ≈ 749 and (105) ≈ 235.

From the two graphs of 00 , we see that 00 has ﬁve zeros. We conclude that is CD on (−∞ −1381), CU on

(−1381 −155), CD on (−155 −103), CU on (−103 060), CD on (060 148), and CU on (148 ∞). There are ﬁve inﬂection points: (−1381 −005), (−155 564), (−103 539), (060 152), and (148 193). c ° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

SECTION 3.6

17. = () =

GRAPHING WITH CALCULUS AND CALCULATORS

¤

149

√

+ 5 sin , ≤ 20.

5 cos + 1

10 cos + 25 sin2 + 10 sin + 26

√

. and 00 = −

4( + 5 sin )32

2 + 5 sin

We’ll start with a graph of () = + 5 sin . Note that () = () is only deﬁned if () ≥ 0. () = 0 ⇔ = 0

From a CAS, 0 =

or ≈ −491, −410, 410, and 491. Thus, the domain of is [−491 −410] ∪ [0 410] ∪ [491 20].

e

From the expression for 0 , we see that 0 = 0 ⇔ 5 cos + 1 = 0 ⇒ 1 = cos−1 − 1 ≈ 177 and

5

al

2 = 2 − 1 ≈ −451 (not in the domain of ). The leftmost zero of 0 is 1 − 2 ≈ −451. Moving to the right, the zeros of 0 are 1 , 1 + 2, 2 + 2, 1 + 4, and 2 + 4. Thus, is increasing on (−491 −451), decreasing on

rS

(−451 −410), increasing on (0 177), decreasing on (177 410), increasing on (491 806), decreasing on (806 1079), increasing on (1079 1434), decreasing on (1434 1708), and increasing on (1708 20). The local maximum values are

and (1708) ≈ 349.

Fo

(−451) ≈ 062, (177) ≈ 258, (806) ≈ 360, and (1434) ≈ 439. The local minimum values are (1079) ≈ 243

is CD on (−491 −410), (0 410), (491 960), CU on (960 1225),

CD on (1225 1581), CU on (1581 1865), and CD on (1865 20). There are

N

19.

ot

inﬂection points at (960 295), (1225 327), (1581 391), and (1865 420).

From the graph of () = sin( + sin 3) in the viewing rectangle [0 ] by [−12 12], it looks like has two maxima and two minima. If we calculate and graph 0 () = [cos( + sin 3)] (1 + 3 cos 3) on [0 2], we see that the graph of 0 appears to be almost tangent to the -axis at about = 07. The graph of

00 = − [sin( + sin 3)] (1 + 3 cos 3)2 + cos( + sin 3)(−9 sin 3) is even more interesting near this -value: it seems to just touch the -axis.

[continued]

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

150

¤

CHAPTER 3

APPLICATIONS OF DIFFERENTIATION

e

If we zoom in on this place on the graph of 00 , we see that 00 actually does cross the axis twice near = 065, indicating a change in concavity for a very short interval. If we look at the graph of 0 on the same interval, we see that it

al

changes sign three times near = 065, indicating that what we had thought was a broad extremum at about = 07 actually

rS

consists of three extrema (two maxima and a minimum). These maximum values are roughly (059) = 1 and (068) = 1, and the minimum value is roughly (064) = 099996. There are also a maximum value of about (196) = 1 and minimum values of about (146) = 049 and (273) = −051. The points of inﬂection on (0 ) are about (061 099998),

Fo

(066 099998), (117 072), (175 077), and (228 034). On ( 2), they are about (401 −034), (454 −077),

(511 −072), (562 −099998), and (567 −099998). There are also IP at (0 0) and ( 0). Note that the function is odd and periodic with period 2, and it is also rotationally symmetric about all points of the form ((2 + 1) 0), an integer.

√

√

(22 + )

4 + 2 = || 2 + ⇒ 0 () = √

4 + 2

⇒ 00 () =

4 (22 + 3)

(4 + 2 )32

N

ot

21. () =

√

-intercepts: When ≥ 0, 0 is the only -intercept. When 0, the -intercepts are ± −.

-intercept = (0) = 0 when ≥ 0. When 0, there is no -intercept.

is an even function, so its graph is symmetric with respect to the -axis.

0 () =

22 +

22 +

(22 + )

√

= −√ for 0 and √ for 0, so has a corner or “point” at = 0 that gets

2 +

2 +

||

2 +

sharper as increases. There is an absolute minimum at 0 for ≥ 0. There are no other maximums nor minimums.

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

SECTION 3.6

GRAPHING WITH CALCULUS AND CALCULATORS

¤

151

4 (22 + 3)

, so 00 () = 0 ⇒ = ± −32 [only for 0]. 00 changes sign at ± −32, so is

3

2 + )32

|| (

√

√

−32 ∞ , and is CD on − −32 − − and

− −32 . There are

CU on −∞ − −32 and

00 () =

IPs at ± −32 32 4 . The more negative becomes, the farther the IPs move from the origin. The only transitional value is = 0.

23. Note that = 0 is a transitional value at which the graph consists of the -axis. Also, we can see that if we substitute − for ,

will be reﬂected in the -axis, so we investigate only positive values of (except = −1, as a

1 + 2 2

demonstration of this reﬂective property). Also, is an odd function. for all . We calculate 0 () =

lim () = 0, so = 0 is a horizontal asymptote

→±∞

(1 + 2 2 ) − (22 )

(2 2 − 1) 0

=−

. () = 0 ⇔ 2 2 − 1 = 0 ⇔

(1 + 2 2 )2

(1 + 2 2 )2

= ±1. So there is an absolute maximum value of (1) =

1

2

and an absolute minimum value of (−1) = − 1 .

2

e

the function () =

=

(−23 )(1 + 2 2 )2 − (−3 2 + )[2(1 + 2 2 )(22 )]

(1 + 2 2 )4

rS

00 () =

al

These extrema have the same value regardless of , but the maximum points move closer to the -axis as increases.

(−23 )(1 + 2 2 ) + (3 2 − )(42 )

23 (2 2 − 3)

=

2 2 )3

(1 +

(1 + 2 2 )3

√

00 () = 0 ⇔ = 0 or ± 3, so there are inﬂection points at (0 0) and

points approach the -axis.

25. () = + sin

Fo

√

√

at ± 3 ± 34 . Again, the -coordinate of the inﬂection points does not depend on , but as increases, both inﬂection

⇒ 0 () = + cos ⇒ 00 () = − sin

ot

(−) = − (), so is an odd function and its graph is symmetric with respect to the origin.

() = 0 ⇔ sin = −, so 0 is always an -intercept.

N

0 () = 0 ⇔ cos = −, so there is no critical number when || 1. If || ≤ 1, then there are inﬁnitely many critical numbers. If 1 is the unique solution of cos = − in the interval [0 ], then the critical numbers are 2 ± 1 , where ranges over the integers. (Special cases: When = −1, 1 = 0; when = 0, =

;

2

and when = 1, 1 = .)

00 () 0 ⇔ sin 0, so is CD on intervals of the form (2 (2 + 1)). is CU on intervals of the form

((2 − 1) 2). The inﬂection points of are the points ( ), where is an integer.

If ≥ 1, then 0 () ≥ 0 for all , so is increasing and has no extremum. If ≤ −1, then 0 () ≤ 0 for all , so is decreasing and has no extremum. If || 1, then 0 () 0 ⇔ cos − ⇔ is in an interval of the form

(2 − 1 2 + 1 ) for some integer . These are the intervals on which is increasing. Similarly, we ﬁnd that is decreasing on the intervals of the form (2 + 1 2( + 1) − 1 ). Thus, has local maxima at the points

√

2 + 1 , where has the values (2 + 1 ) + sin 1 = (2 + 1 ) + 1 − 2 , and has local minima at the points

√

2 − 1 , where we have (2 − 1 ) = (2 − 1 ) − sin 1 = (2 − 1 ) − 1 − 2 .

[continued]

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

152

¤

CHAPTER 3

APPLICATIONS OF DIFFERENTIATION

The transitional values of are −1 and 1. The inﬂection points move vertically, but not horizontally, when changes.

When || ≥ 1, there is no extremum. For || 1, the maxima are spaced

2 apart horizontally, as are the minima. The horizontal spacing between maxima and adjacent minima is regular (and equals ) when = 0, but the horizontal space between a local maximum and the nearest local minimum shrinks as || approaches 1.

27. (a) () = 4 − 22 + 1. For = 0, () = −22 + 1, a parabola whose vertex, (0 1), is the absolute maximum. For

0, () = 4 − 22 + 1 opens upward with two minimum points. As → 0, the minimum points spread apart and move downward; they are below the -axis for 0 1 and above for 1. For 0, the graph opens downward, and

e

has an absolute maximum at = 0 and no local minimum.

al

(b) 0 () = 43 − 4 = 4(2 − 1) [ 6= 0]. If ≤ 0, 0 is the only critical number.

00 () = 122 − 4, so 00 (0) = −4 and there is a local maximum at

rS

(0 (0)) = (0 1), which lies on = 1 − 2 . If 0, the critical

√

numbers are 0 and ±1 . As before, there is a local maximum at

Fo

(0 (0)) = (0 1), which lies on = 1 − 2 .

√

00 ±1 = 12 − 4 = 8 0, so there is a local minimum at

√

√

= ±1 . Here ±1 = (12 ) − 2 + 1 = −1 + 1.

ot

√

√ 2

But ±1 −1 + 1 lies on = 1 − 2 since 1 − ±1

= 1 − 1.

3.7 Optimization Problems

First Number

1

Second Number

N

1. (a)

Product

22

22

21

42

3

20

60

4

19

18

90

6

17

102

7

16

112

8

15

than the second, since we can just interchange the numbers

76

5

We needn’t consider pairs where the ﬁrst number is larger

120

2

9

14

13

130

11

12

have considered only integers in the table.

126

10

in such cases. The answer appears to be 11 and 12, but we

132

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

SECTION 3.7

OPTIMIZATION PROBLEMS

¤

153

(b) Call the two numbers and . Then + = 23, so = 23 − . Call the product . Then

= = (23 − ) = 23 − 2 , so we wish to maximize the function () = 23 − 2 . Since 0 () = 23 − 2, we see that 0 () = 0 ⇔ =

23

2

= 115. Thus, the maximum value of is (115) = (115)2 = 13225 and it

occurs when = = 115.

Or: Note that 00 () = −2 0 for all , so is everywhere concave downward and the local maximum at = 115 must be an absolute maximum.

3. The two numbers are and

100

100

2 − 100

100

. The critical

, where 0. Minimize () = +

. 0 () = 1 − 2 =

2

number is = 10. Since 0 () 0 for 0 10 and 0 () 0 for 10, there is an absolute minimum at = 10.

The numbers are 10 and 10.

0 () = 1 − 2 = 0 ⇔ = 1 . (−1) = 0,

2

1

2

e

5. Let the vertical distance be given by () = ( + 2) − 2 , −1 ≤ ≤ 2.

= 9 , and (2) = 0, so

4

rS

al

there is an absolute maximum at = 1 . The maximum distance is

2

1 1

1

9

2 = 2 + 2 − 4 = 4.

7. If the rectangle has dimensions and , then its perimeter is 2 + 2 = 100 m, so = 50 − . Thus, the area is

= = (50 − ). We wish to maximize the function () = (50 − ) = 50 − 2 , where 0 50. Since

Fo

0 () = 50 − 2 = −2( − 25), 0 () 0 for 0 25 and 0 () 0 for 25 50. Thus, has an absolute maximum at = 25, and (25) = 252 = 625 m2 . The dimensions of the rectangle that maximize its area are = = 25 m.

(The rectangle is a square.)

0 () =

() =

1 + 2

⇒

ot

9. We need to maximize for ≥ 0.

(1 + 2 ) − (2)

(1 − 2 )

(1 + )(1 − )

=

=

. 0 () 0 for 0 1 and 0 () 0

2 )2

(1 +

(1 + 2 )2

(1 + 2 )2

11. (a)

N

for 1. Thus, has an absolute maximum of (1) = 1 at = 1.

2

The areas of the three ﬁgures are 12,500, 12,500, and 9000 ft2 . There appears to be a maximum area of at least 12,500 ft2 .

(b) Let denote the length of each of two sides and three dividers.

Let denote the length of the other two sides.

(c) Area = length × width = ·

(d) Length of fencing = 750 ⇒ 5 + 2 = 750

(e) 5 + 2 = 750 ⇒ = 375 − 5 ⇒ () = 375 − 5 = 375 − 5 2

2

2

2

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

154

¤

CHAPTER 3

APPLICATIONS OF DIFFERENTIATION

(f ) 0 () = 375 − 5 = 0 ⇒ = 75. Since 00 () = −5 0 there is an absolute maximum when = 75. Then

= 375 = 1875. The largest area is 75 375 = 14,0625 ft2 . These values of and are between the values in the ﬁrst

2

2 and second ﬁgures in part (a). Our original estimate was low.

= 15 × 106 , so = 15 × 106. Minimize the amount of fencing, which is

13.

3 + 2 = 3 + 2(15 × 106) = 3 + 3 × 106 = ().

0 () = 3 − 3 × 1062 = 3(2 − 106 )2 . The critical number is = 103 and

0 () 0 for 0 103 and 0 () 0 if 103 , so the absolute minimum occurs when = 103 and = 15 × 103 .

The ﬁeld should be 1000 feet by 1500 feet with the middle fence parallel to the short side of the ﬁeld.

15. Let be the length of the base of the box and the height. The surface area is 1200 = 2 + 4

⇒ = (1200 − 2 )(4).

al

e

The volume is = 2 = 2 (1200 − 2 )4 = 300 − 34 ⇒ 0 () = 300 − 3 2 .

4

√

0

2

0

3 2

⇒ = 400 ⇒ = 400 = 20. Since () 0 for 0 20 and 0 () 0 for

() = 0 ⇒ 300 = 4

20, there is an absolute maximum when = 20 by the First Derivative Test for Absolute Extreme Values (see page 253).

rS

If = 20, then = (1200 − 202 )(4 · 20) = 10, so the largest possible volume is 2 = (20)2 (10) = 4000 cm3 .

10 = (2)() = 22 , so = 52 . The cost is

17.

() = 10(22 ) + 6[2(2) + 2] + 6(22 )

Fo

= 322 + 36 = 322 + 180

0 () = 64 − 1802 = 4(163 − 45)2

3

45

.

16

The minimum cost is

3

45

16

ot

0 () 0 for

⇒ =

3

45

16

is the critical number. 0 () 0 for 0

√

= 32(28125)23 + 180 3 28125 ≈ $19128.

19. The distance from the origin (0 0) to a point ( 2 + 3) on the line is given by =

3

45

16

and

( − 0)2 + (2 + 3 − 0)2 and the

square of the distance is = 2 = 2 + (2 + 3)2 . 0 = 2 + 2(2 + 3)2 = 10 + 12 and 0 = 0 ⇔ = − 6 . Now

5

6

6 3

00 = 10 0, so we know that has a minimum at = − 6 . Thus, the -value is 2 − 5 + 3 = 3 and the point is − 5 5 .

5

5

N

21.

From the ﬁgure, we see that there are two points that are farthest away from

(1 0). The distance from to an arbitrary point ( ) on the ellipse is

= ( − 1)2 + ( − 0)2 and the square of the distance is

= 2 = 2 − 2 + 1 + 2 = 2 − 2 + 1 + (4 − 42 ) = −32 − 2 + 5.

0 = −6 − 2 and 0 = 0 ⇒ = − 1 . Now 00 = −6 0, so we know

3

that has a maximum at = − 1 . Since −1 ≤ ≤ 1, (−1) = 4,

3

1

− 3 = 16 , and (1) = 0, we see that the maximum distance is 16 . The corresponding -values are

3

3

√

√

2

= ± 4 − 4 − 1 = ± 32 = ± 4 2 ≈ ±189. The points are − 1 ± 4 2 .

3

9

3

3

3

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

SECTION 3.7

¤

OPTIMIZATION PROBLEMS

The area of the rectangle is (2)(2) = 4. Also 2 = 2 + 2 so

√

√

= 2 − 2 , so the area is () = 4 2 − 2 . Now

√

2

2 − 22

2 − 2 − √

. The critical number is

0 () = 4

=4√

2 − 2

2 − 2

23.

=

=

2 −

and 2 =

1

√

2

√

2 .

2

=

1 2

2

=

1

√

2

1

√ .

2

Clearly this gives a maximum.

= , which tells us that the rectangle is a square. The dimensions are 2 =

The height of the equilateral triangle with sides of length is

25.

since 2 + (2)2 = 2

√

3 =

Using similar triangles,

√

3

2

3

2

−

√

3

2

e

√

3

.

2

√

=

−

=

2

√

⇒ = 23 − 3 ⇒ =

√

al

=

⇒ 2 = 2 − 1 2 = 3 2

4

4

√

3

2

√

2

,

⇒

√

3 ⇒

√

3

2 (

− 2).

√

3

2

−

√

3

4

=

√

3

,

4

so the dimensions are 2 and

Fo

= 4, and =

rS

√

√

√

The area of the inscribed rectangle is () = (2) = 3 ( − 2) = 3 − 2 3 2 , where 0 ≤ ≤ 2. Now

√

√

√ √

0 = 0 () = 3 − 4 3 ⇒ = 3 4 3 = 4. Since (0) = (2) = 0, the maximum occurs when

√

3

.

4

The area of the triangle is

27.

ot

() = 1 (2)( + ) = ( + ) =

2

N

√

2 +

√

= 2 − 2

2 − 2

√

2 − 2 ( + ). Then

√

−2

−2

0 = 0 () = √

+ 2 − 2 + √

2 − 2

2

2 2 − 2

√

2 +

= −√

+ 2 − 2 ⇒

2 − 2

⇒ 2 + = 2 − 2

⇒ 0 = 22 + − 2 = (2 − )( + ) ⇒

= 1 or = −. Now () = 0 = (−) ⇒ the maximum occurs where = 1 , so the triangle has

2

2

√

1 2 height + 1 = 3 and base 2 2 − 2 = 2 3 2 = 3 .

2

2

4

29.

The cylinder has volume = 2 (2). Also 2 + 2 = 2

⇒ 2 = 2 − 2 , so

() = (2 − 2 )(2) = 2(2 − 3 ), where 0 ≤ ≤ .

√

0 () = 2 2 − 32 = 0 ⇒ = 3. Now (0) = () = 0, so there is a

√

√

√

√ maximum when = 3 and 3 = (2 − 2 3) 2 3 = 43 3 3 .

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

155

156

¤

CHAPTER 3

APPLICATIONS OF DIFFERENTIATION

The cylinder has surface area

31.

2(area of the base) + (lateral surface area) = 2(radius)2 + 2(radius)(height)

= 22 + 2(2)

√

= 2 − 2 , so the surface area is

√

() = 2(2 − 2 ) + 4 2 − 2 0 ≤ ≤

√

= 22 − 22 + 4 2 − 2

0 () = 0 − 4 + 4 · 1 (2 − 2 )−12 (−2) + (2 − 2 )12 · 1

Thus,

2

√

√

2

− 2 − 2 − 2 + 2 − 2

2 − 2

√

= 4 − − √

= 4 ·

+

2 − 2

2 − 2

√

√

2

0 () = 0 ⇒ 2 − 2 = 2 − 22 () ⇒ 2 − 2 = (2 − 22 )2 ⇒

2 (2 − 2 ) = 4 − 42 2 + 44

⇒ 2 = 2 − 2

⇒

⇒ 2 2 − 4 = 4 − 42 2 + 44

√

5± 5 2

,

10

but we reject the root with the + sign since it

√ doesn’t satisfy (). [The right side is negative and the left side is positive.] So = 5 − 5 . Since (0) = () = 0, the

10

the surface area is

√ √

√

2 5 + 5 2 + 4 5 − 5 5 + 5 2 = 2 2 ·

10

10

10

√

5− 5 2

10

⇒ 2 = 2 −

rS

maximum surface area occurs at the critical number and 2 =

al

This is a quadratic equation in 2 . By the quadratic formula, 2 =

⇒ 54 − 52 2 + 4 = 0.

e

Now 2 + 2 = 2

√

5+ 5

10

+4

√

(5−

√

5)(5+ 5)

10

Fo

√

√

2 5+ 5 + 2·2 5

5

=

= 2

√

5+5 5

5

= 2

√

5− 5 2

10

√

5+ 5

5

+

=

√

5+ 5 2

10

⇒

√

2 20

5

√

= 2 1 + 5 .

= 384 ⇒ = 384. Total area is

33.

ot

() = (8 + )(12 + 384) = 12(40 + + 256), so

0 () = 12(1 − 2562 ) = 0 ⇒ = 16. There is an absolute minimum

N

when = 16 since 0 () 0 for 0 16 and 0 () 0 for 16.

When = 16, = 38416 = 24, so the dimensions are 24 cm and 36 cm.

Let be the length of the wire used for the square. The total area is

2 1 10 − √3 10 −

+

() =

4

2

3

2

3

35.

=

√

√

√

1 2

16

+

√

3

36 (10

− )2 , 0 ≤ ≤ 10

√

3

9

3

0 () = 1 − 18 (10 − ) = 0 ⇔ 72 + 4723 − 40 3 = 0 ⇔ = 9 40 4√3 .

8

72

+

√

√

3

3

Now (0) = 36 100 ≈ 481, (10) = 100 = 625 and 9 40 4√3 ≈ 272, so

16

+

(a) The maximum area occurs when = 10 m, and all the wire is used for the square.

(b) The minimum area occurs when =

√

40 √

3

9+4 3

≈ 435 m.

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

SECTION 3.7

37.

OPTIMIZATION PROBLEMS

¤

The volume is = 2 and the surface area is

2

= 2 +

.

() = 2 + 2 = 2 + 2

2

2

0

3

() = 2 − 2 = 0 ⇒ 2 = 2 ⇒ = 3 cm.

This gives an absolute minimum since 0 () 0 for 0 3 and 0 () 0 for 3

.

3

When =

,=

cm.

=

= 3

2

()23

2 + 2 = 2

39.

0 () =

⇒ =

(2

3

2

3

=

2

3 (

− 32 ) = 0 when =

− 2 ) =

1

√ .

3

2

3 (

− 3 ).

This gives an absolute maximum, since

1

√ .

3

The maximum volume is

By similar triangles,

−

=

(1). The volume of the inner cone is = 1 2 ,

3

rS

41.

al

e

1

0 () 0 for 0 √3 and 0 () 0 for

1

1

1

2

√3 = √3 3 − 3√3 3 = 9√3 3 .

3

so we’ll solve (1) for .

−

=

= ( − ) (2).

2

· ( − ) =

(2 − 3 ) ⇒

3

3

Fo

=−

= − ⇒

Thus, () =

(2 − 32 ) =

(2 − 3).

3

3

1 1

0 () = 0 ⇒ = 0 or 2 = 3 ⇒ = 2 and from (2), =

= 3 .

− 2 =

3

3

3

0 () changes from positive to negative at = 2 , so the inner cone has a maximum volume of

3

2 2 1

2

2

1

1

4

1

= 27 · 3 , which is approximately 15% of the volume of the larger cone.

= 3 = 3 3

3

N

ot

0 () =

43. () =

2

( + )2

⇒

0 () =

=

0 () = 0 ⇒ =

( + )2 · 2 − 2 · 2( + )

(2 + 2 + 2 ) 2 − 2 2 2 − 2 2

=

2 ]2

[( + )

( + )4

2 2 − 2 2

2 (2 − 2 )

2 ( + )( − )

2 ( − )

=

=

=

( + )4

( + )4

( + )4

( + )3

⇒ () =

2

2

2

=

=

.

2

2

( + )

4

4

The expression for 0 () shows that 0 () 0 for and 0 () 0 for . Thus, the maximum value of the power is 2 (4), and this occurs when = .

45. = 6 − 3 2 cot + 32

2

(a)

√

3

2

csc

√

√

= 3 2 csc2 − 32 23 csc cot or 3 2 csc csc − 3 cot .

2

2

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

157

158

¤

(b)

CHAPTER 3

APPLICATIONS OF DIFFERENTIATION

√

= 0 when csc − 3 cot = 0 ⇒

√ cos

1

− 3

= 0 ⇒ cos = sin sin

1

that the minimum surface area occurs when = cos−1 √3 ≈ 55◦ .

(c)

If cos =

1

√ ,

3

then cot =

1

= 6 − 3 2 √2 +

2

1

√

2

and csc =

√

√3 ,

2

√ √

32 23 √3

2

= 6 −

6

1

= 6 + 2√2 2 = 6 + 2√2

The First Derivative Test shows

so the surface area is

3

√ 2

2 2

+

9

√ 2

2 2

√

√

2 + 25

5−

1

+

, 0 ≤ ≤ 5 ⇒ 0 () = √

− = 0 ⇔ 8 = 6 2 + 25 ⇔

2 + 25

6

8

8

6

162 = 9(2 + 25) ⇔ =

15

√ .

7

But

15

√

7

5, so has no critical number. Since (0) ≈ 146 and (5) ≈ 118, he

e

47. Here () =

1

√ .

3

49. There are (6 − ) km over land and

√

2 + 4 km under the river.

al

should row directly to .

rS

We need to minimize the cost (measured in $100,000) of the pipeline.

√

2 + 4 (8) ⇒

() = (6 − )(4) +

8

.

0 () = −4 + 8 · 1 (2 + 4)−12 (2) = −4 + √

2

2 + 4

ot

Fo

√

8

0 () = 0 ⇒ 4 = √

2 + 4 = 2 ⇒ 2 + 4 = 42 ⇒ 4 = 32 ⇒ 2 = 4 ⇒

⇒

3

2 +4

√

√

= 2 3 [0 ≤ ≤ 6]. Compare the costs for = 0, 2 3, and 6. (0) = 24 + 16 = 40,

√

√

√

√

√

2 3 = 24 − 8 3 + 32 3 = 24 + 24 3 ≈ 379, and (6) = 0 + 8 40 ≈ 506. So the minimum cost is about

√

$379 million when is 6 − 2 3 ≈ 485 km east of the reﬁnery.

The total illumination is () =

N

51.

0 () =

3

+

, 0 10. Then

2

(10 − )2

−6

2

+

= 0 ⇒ 6(10 − )3 = 23

3

(10 − )3

⇒

√

√

√

√

√

3

3 (10 − ) = ⇒ 10 3 3 − 3 3 = ⇒ 10 3 3 = + 3 3 ⇒

√

√

√

10 3 3

√ ≈ 59 ft. This gives a minimum since 00 () 0 for 0 10.

10 3 3 = 1 + 3 3 ⇒ =

1+ 33

3(10 − )3 = 3

53.

⇒

Every line segment in the ﬁrst quadrant passing through ( ) with endpoints on the and -axes satisﬁes an equation of the form − = ( − ), where 0. By setting

= 0 and then = 0, we ﬁnd its endpoints, (0 − ) and − 0 . The

distance from to is given by = [ − − 0]2 + [0 − ( − )]2 .

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

SECTION 3.7

OPTIMIZATION PROBLEMS

¤

159

It follows that the square of the length of the line segment, as a function of , is given by

2

2

2

+ ( − )2 = 2 −

() = −

+ 2 + 2 2 − 2 + 2 . Thus,

2

22

2

− 3 + 22 − 2 = 3 ( − 2 + 2 4 − 3 )

2

2

2

= 3 [( − ) + 3 ( − )] = 3 ( − )( + 3 )

2

Thus, 0 () = 0 ⇔ = or = − 3 . Since 0 and 0, must equal − 3 . Since 3 0, we see

that 0 () 0 for − 3 and 0 () 0 for − 3 . Thus, has its absolute minimum value when = − 3 .

0 () =

That value is

2

2

2 √

2

√

3

3 2

+ − 3 − = + 2 +

+

−3 = + 3

e

= 2 + 243 23 + 23 43 + 43 23 + 223 43 + 2 = 2 + 343 23 + 323 43 + 2

[= ( + )3 ] with = 23 and = 23 ,

√

so we can write it as (23 + 23 )3 and the shortest such line segment has length = (23 + 23 )32 .

−

3

⇒ 0 = −

3

3

, so an equation of the tangent line at the point ( ) is

2

rS

55. =

al

The last expression is of the form 3 + 32 + 3 2 + 3

3

6

3

3

= − 2 ( − ), or = − 2 + . The -intercept [ = 0] is 6. The

-intercept [ = 0] is 2. The distance of the line segment that has endpoints at the

36

(2 − 0)2 + (0 − 6)2 . Let = 2 , so = 42 + 2

Fo

intercepts is =

⇒

√

72

= 8 ⇔ 4 = 9 ⇔ 2 = 3 ⇒ = 3.

3

√

216

00 = 8 + 4 0, so there is an absolute minimum at = 3 Thus, = 4(3) + 36 = 12 + 12 = 24 and

3

√

√ hence, = 24 = 2 6.

72

. 0 = 0 ⇔

3

ot

0 = 8 −

()

0 () − ()

, then, by the Quotient Rule, we have 0 () =

. Now 0 () = 0 when

2

N

57. (a) If () =

()

= (). Therefore, the marginal cost equals the average cost.

√

(b) (i) () = 16,000 + 200 + 432 , (1000) = 16,000 + 200,000 + 40,000 10 ≈ 216,000 + 126,491, so

0 () − () = 0 and this gives 0 () =

(1000) ≈ $342,491. () = () =

0 (1000) = 200 + 60

16,000

+ 200 + 412 , (1000) ≈ $34249unit. 0 () = 200 + 612 ,

√

10 ≈ $38974unit.

(ii) We must have 0 () = () ⇔ 200 + 612 =

16,000

+ 200 + 412

⇔ 232 = 16,000 ⇔

= (8,000)23 = 400 units. To check that this is a minimum, we calculate

0 () =

2

−16,000

2

+ √ = 2 (32 − 8000). This is negative for (8000)23 = 400, zero at = 400,

2

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

160

¤

CHAPTER 3

APPLICATIONS OF DIFFERENTIATION

and positive for 400, so is decreasing on (0 400) and increasing on (400 ∞). Thus, has an absolute minimum at = 400. [Note: 00 () is not positive for all 0.]

(iii) The minimum average cost is (400) = 40 + 200 + 80 = $320unit.

59. (a) We are given that the demand function is linear and (27,000) = 10, (33,000) = 8, so the slope is

10 − 8

27,000 − 33,000

1

1

= − 3000 and an equation of the line is − 10 = − 3000 ( − 27,000) ⇒

1

= () = − 3000 + 19 = 19 − (3000).

(b) The revenue is () = () = 19 − (23000) ⇒ 0 () = 19 − (1500) = 0 when = 28,500. Since

00 () = −11500 0, the maximum revenue occurs when = 28,500 ⇒ the price is (28,500) = $950.

61. (a) As in Example 6, we see that the demand function is linear. We are given that (1000) = 450 and deduce that

1

1

so an equation is − 450 = − 10 ( − 1000) or () = − 10 + 550.

440 − 450

1100 − 1000

1

= − 10 ,

e

(1100) = 440, since a $10 reduction in price increases sales by 100 per week. The slope for is

(2750) = 275, so the rebate should be 450 − 275 = $175.

al

1

(b) () = () = − 10 2 + 550. 0 () = − 1 + 550 = 0 when = 5(550) = 2750.

5

rS

1

1

(c) () = 68,000 + 150 ⇒ () = () − () = − 10 2 + 550 − 68,000 − 150 = − 10 2 + 400 − 68,000,

0 () = − 1 + 400 = 0 when = 2000. (2000) = 350. Therefore, the rebate to maximize proﬁts should be

5

Fo

450 − 350 = $100.

Here 2 = 2 + 24, so 2 = 2 − 24. The area is = 1

2

63.

ot

Let the perimeter be , so 2 + = or = ( − )2 ⇒

() = 1 ( − )24 − 24 = 2 − 24. Now

2

2 − 2

4

−3 + 2

0

−

() =

=

.

4

2 − 2

4 2 − 2

2 − 24.

N

Therefore, 0 () = 0 ⇒ −3 + 2 = 0 ⇒ = 3. Since 0 () 0 for 3 and 0 () 0 for 3, there is an absolute maximum when = 3. But then 2 + 3 = , so = 3 ⇒ = ⇒ the triangle is equilateral.

65. Note that || = | | + | |

⇒ 5 = + | | ⇒ | | = 5 − .

Using the Pythagorean Theorem for ∆ and ∆ gives us

() = | | + | | + | | = + (5 − )2 + 22 + (5 − )2 + 32

√

√

= + 2 − 10 + 29 + 2 − 10 + 34 ⇒

−5

−5

0 () = 1 + √

+√

. From the graphs of

2 − 10 + 29

2 − 10 + 34 and 0 , it seems that the minimum value of is about (359) = 935 m.

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

SECTION 3.7

OPTIMIZATION PROBLEMS

¤

161

The total time is

67.

() = (time from to ) + (time from to )

√

2 + ( − )2

2 + 2

+

, 0

=

1

2

0 () =

−

sin 1 sin 2

√

−

=

−

1

2

1 2 + 2

2 2 + ( − )2

The minimum occurs when 0 () = 0 ⇒

sin 1 sin 2

=

.

1

2

[Note: 00 () 0]

2 = 2 + 2 , but triangles and are similar, so

√

√

8 = 4 − 4

⇒ = 2 − 4. Thus, we minimize

69.

( − 4)(32 ) − 3

2 [3( − 4) − ]

22 ( − 6)

=

=

=0

2

2

( − 4)

( − 4)

( − 4)2

al

0 () =

e

() = 2 = 2 + 42 ( − 4) = 3 ( − 4), 4 ≤ 8.

rS

when = 6. 0 () 0 when 6, 0 () 0 when 6, so the minimum occurs when = 6 in.

It sufﬁces to maximize tan . Now

71.

Fo

3 tan + tan

+ tan

= tan( + ) =

=

. So

1

1 − tan tan

1 − tan

3(1 − tan ) = + tan

=

1

√

3

2

.

1 + 32

2 1 + 32 − 2(6)

2 1 − 32

⇒ () =

=

= 0 ⇔ 1 − 32 = 0 ⇔

(1 + 32 )2

(1 + 32 )2

since ≥ 0. Now 0 () 0 for 0 ≤

√

2 1 3

1

and tan =

√ 2 = √

3

1 + 3 1 3

√

⇒ = .

3 = tan +

6

6

N

73.

⇒ tan =

0

ot

2

Let () = tan =

1 + 32

⇒ 2 = (1 + 32 ) tan

⇒ =

1

√

3

6.

and 0 () 0 for

1

√ ,

3

so has an absolute maximum when =

1

√

3

Substituting for and in 3 = tan( + ) gives us

In the small triangle with sides and and hypotenuse , sin =

and

cos =

. In the triangle with sides and and hypotenuse , sin = and

cos =

. Thus, = sin , = cos , = sin , and = cos , so the

area of the circumscribed rectangle is

[continued]

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

162

¤

CHAPTER 3

APPLICATIONS OF DIFFERENTIATION

() = ( + )( + ) = ( sin + cos )( cos + sin )

= 2 sin cos + sin2 + cos2 + 2 sin cos

= sin2 + cos2 + (2 + 2 ) sin cos

= (sin2 + cos2 ) + (2 + 2 ) ·

1

2

· 2 sin cos = + 1 (2 + 2 ) sin 2, 0 ≤ ≤

2

This expression shows, without calculus, that the maximum value of () occurs when sin 2 = 1 ⇔ 2 =

= . So the maximum area is = + 1 (2 + 2 ) = 1 (2 + 2 + 2 ) = 1 ( + )2 .

4

4

2

2

2

75. (a)

2

2

⇒

If = energykm over land, then energykm over water = 14.

√

So the total energy is = 14 25 + 2 + (13 − ), 0 ≤ ≤ 13,

and so

= 0: 14 = (25 + 2 )12

⇒ 1962 = 2 + 25 ⇒ 0962 = 25 ⇒ =

√5

096

e

Set

14

=

− .

(25 + 2 )12

≈ 51.

al

Testing against the value of at the endpoints: (0) = 14(5) + 13 = 20, (51) ≈ 179, (13) ≈ 195.

Thus, to minimize energy, the bird should ﬂy to a point about 51 km from .

rS

(b) If is large, the bird would ﬂy to a point that is closer to than to to minimize the energy used ﬂying over water.

Fo

If is small, the bird would ﬂy to a point that is closer to than to to minimize the distance of the ﬂight.

√

√

25 + 2

2 + (13 − ) ⇒

= √

=

. By the same sort of

− = 0 when

= 25 +

25 + 2 argument as in part (a), this ratio will give the minimal expenditure of energy if the bird heads for the point km from .

(c) For ﬂight direct to , = 13, so from part (b), =

√

25 + 132

13

≈ 107. There is no value of for which the bird

should ﬂy directly to . But note that lim () = ∞, so if the point at which is a minimum is close to , then

is large.

ot

→0+

N

(d) Assuming that the birds instinctively choose the path that minimizes the energy expenditure, we can use the equation for

√

= 0 from part (a) with 14 = , = 4, and = 1: (4) = 1 · (25 + 42 )12 ⇒ = 414 ≈ 16.

3.8 Newton's Method

1. (a)

The tangent line at = 1 intersects the -axis at ≈ 23, so

2 ≈ 23. The tangent line at = 23 intersects the -axis at

≈ 3, so 3 ≈ 30.

(b) 1 = 5 would not be a better ﬁrst approximation than 1 = 1 since the tangent line is nearly horizontal. In fact, the second approximation for 1 = 5 appears to be to the left of = 1.

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

SECTION 3.8 NEWTON’S METHOD

¤

163

3. Since the tangent line = 9 − 2 is tangent to the curve = () at the point (2 5), we have 1 = 2, (1 ) = 5, and

0 (1 ) = −2 [the slope of the tangent line]. Thus, by Equation 2,

2 = 1 −

Note that geometrically

9

2

(1 )

5

9

=2−

=

0 (1 )

−2

2

represents the -intercept of the tangent line = 9 − 2.

5. The initial approximations 1 = , and will work, resulting in a second approximation closer to the origin, and lead to the

root of the equation () = 0, namely, = 0. The initial approximation 1 = will not work because it will result in

5 − − 1

. Now 1 = 1 ⇒

54 − 1

(125)5 − 125 − 1

1−1−1

= 1 − − 1 = 125 ⇒ 3 = 125 −

≈ 11785.

4

5−1

5(125)4 − 1

9. () = 3 + + 3

Now 1 = −1 ⇒

0 () = 32 + 1, so +1 = −

3 + + 3

32 + 1

(−1)3 + (−1) + 3

−1 − 1 + 3

1

= −1 −

= −1 − = −125.

3(−1)2 + 1

3+1

4

ot

2 = −1 −

⇒

Fo

2 = 1 −

⇒ 0 () = 54 − 1, so +1 = −

rS

7. () = 5 − − 1

al

e

successive approximations farther and farther from the origin.

Newton’s method follows the tangent line at (−1 1) down to its intersection with

N

the -axis at (−125 0), giving the second approximation 2 = −125.

11. To approximate =

+1 = −

√

5

20 (so that 5 = 20), we can take () = 5 − 20. So 0 () = 54 , and thus,

√

5 − 20

. Since 5 32 = 2 and 32 is reasonably close to 20 we’ll use 1 = 2. We need to ﬁnd approximations

54

until they agree to eight decimal places. 1 = 2 ⇒ 2 = 185, 3 ≈ 182148614, 4 ≈ 182056514,

√

5 ≈ 182056420 ≈ 6 . So 5 20 ≈ 182056420, to eight decimal places.

Here is a quick and easy method for ﬁnding the iterations for Newton’s method on a programmable calculator.

(The screens shown are from the TI-84 Plus, but the method is similar on other calculators.) Assign () = 5 − 20 to Y1 , and 0 () = 54 to Y2 . Now store 1 = 2 in X and then enter X − Y1 Y2 → X to get 2 = 185. By successively pressing the ENTER key, you get the approximations 3 , 4 , .

[continued]

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

164

¤

CHAPTER 3

APPLICATIONS OF DIFFERENTIATION

In Derive, load the utility ﬁle SOLVE. Enter NEWTON(xˆ5-20,x,2) and then APPROXIMATE to get

[2, 1.85, 1.82148614, 1.82056514, 1.82056420]. You can request a speciﬁc iteration by adding a fourth argument. For example, NEWTON(xˆ5-20,x,2,2) gives [2 185 182148614].

In Maple, make the assignments := → ˆ5 − 20;, := → − ()()();, and := 2;. Repeatedly execute the command := (); to generate successive approximations.

In Mathematica, make the assignments [_ ] := ˆ5 − 20, [_ ] := − [] 0 [], and = 2 Repeatedly execute the

4 − 23 + 52 − 6

. We need to ﬁnd

43 − 62 + 10

⇒ 0 () = 43 − 62 + 10 ⇒ +1 = −

al

13. () = 4 − 23 + 52 − 6

e

command = [] to generate successive approximations.

rS

approximations until they agree to six decimal places. We’ll let 1 equal the midpoint of the given interval, [1 2].

1 = 15 ⇒ 2 = 12625, 3 ≈ 1218808, 4 ≈ 1217563, 5 ≈ 1217562 ≈ 6 . So the root is 1217562 to six decimal places. +1 = −

⇒ 0 () = cos − 2 ⇒

Fo

15. sin = 2 , so () = sin − 2

sin − 2

. From the ﬁgure, the positive root of sin = 2 is cos − 2

near 1. 1 = 1 ⇒ 2 ≈ 0891396, 3 ≈ 0876985, 4 ≈ 0876726 ≈ 5 . So

From the graph, we see that there appear to be points of intersection near

= −4, = −2, and = 1. Solving 3 cos = + 1 is the same as solving

N

17.

ot

the positive root is 0876726, to six decimal places.

() = 3 cos − − 1 = 0. 0 () = −3 sin − 1, so

+1 = −

3 cos − − 1

.

−3 sin − 1

1 = −4

1 = −2

1 = 1

2 ≈ −3682281

2 ≈ −1856218

2 ≈ 0892438

3 ≈ −3638960

3 ≈ −1862356

3 ≈ 0889473

4 ≈ −3637959

4 ≈ −1862365 ≈ 5

4 ≈ 0889470 ≈ 5

5 ≈ −3637958 ≈ 6

To six decimal places, the roots of the equation are −3637958, −1862365, and 0889470.

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

SECTION 3.8 NEWTON’S METHOD

¤

From the graph, we see that there appear to be points of intersection near

√

= −05 and = 15. Solving 3 = 2 − 1 is the same as solving

√

√

3

3

() = − 2 + 1 = 0. () = − 2 + 1 ⇒

√

3

− 2 + 1

0

1 −23

− 2, so +1 = − 1 −23

.

() = 3

− 2

3

19.

1 = −05

1 = 15

2 ≈ −0471421

2 ≈ 461653

3 ≈ −0471074 ≈ 4

3 ≈ 1461070 ≈ 4

To six decimal places, the roots are −0471074 and 1461070.

21. From the graph, there appears to be a point of intersection near = 06.

√

√

is the same as solving () = cos − = 0.

√

√

() = cos − ⇒ 0 () = − sin − 1 2 , so

al

√

√ . Now 1 = 06 ⇒ 2 ≈ 0641928,

− sin − 1 2 cos −

rS

+1 = −

e

Solving cos =

3 ≈ 0641714 ≈ 4 . To six decimal places, the root of the equation is 0641714.

() = 6 − 5 − 64 − 2 + + 10 ⇒

23.

Fo

0 () = 65 − 54 − 243 − 2 + 1 ⇒

+1 = −

6 − 5 − 64 − 2 + + 10

.

65 − 54 − 243 − 2 + 1

From the graph of , there appear to be roots near −19, −12, 11, and 3.

1 = −19

1 = 11

1 = 3

2 ≈ −122006245

2 ≈ 114111662

2 ≈ 299

3 ≈ −193828380

3 ≈ −121997997 ≈ 4

3 ≈ 113929741

3 ≈ 298984106

4 ≈ 113929375 ≈ 5

4 ≈ 298984102 ≈ 5

ot

1 = −12

2 ≈ −194278290

N

4 ≈ −193822884

5 ≈ −193822883 ≈ 6

To eight decimal places, the roots of the equation are −193822883, −121997997, 113929375, and 298984102.

25.

165

Solving

√

1 − 2

1

− 1 − = 0. 0 () = 2

+ √

+1

( + 1)2

2 1−

√

− 1 −

2 +1

= −

.

1

1 − 2

+ √

2 1 −

(2 + 1)2

() =

+1

√

= 1 − is the same as solving

2 + 1

2

⇒

From the graph, we see that the curves intersect at about 08. 1 = 08 ⇒ 2 ≈ 076757581, 3 ≈ 076682610,

4 ≈ 076682579 ≈ 5 . To eight decimal places, the root of the equation is 076682579.

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

166

¤

CHAPTER 3

APPLICATIONS OF DIFFERENTIATION

27. (a) () = 2 −

+1 = −

⇒ 0 () = 2, so Newton’s method gives

2 −

1

1

1

= − +

= +

=

.

+

2

2

2

2

2

2

(b) Using (a) with = 1000 and 1 =

So

√

1000 ≈ 31622777.

29. () = 3 − 3 + 6

√

900 = 30, we get 2 ≈ 31666667, 3 ≈ 31622807, and 4 ≈ 31622777 ≈ 5 .

⇒ 0 () = 32 − 3. If 1 = 1, then 0 (1 ) = 0 and the tangent line used for approximating 2 is

horizontal. Attempting to ﬁnd 2 results in trying to divide by zero.

31. For () = 13 , 0 () =

1 −23

3

and

13

( )

= − 1 −23 = − 3 = −2 .

0 ( )

3

Therefore, each successive approximation becomes twice as large as the

2 = −2(05) = −1, and 3 = −2(−1) = 2.

33. (a) () = 6 − 4 + 33 − 2

rS

converge to the root, which is 0. In the ﬁgure, we have 1 = 05,

al

previous one in absolute value, so the sequence of approximations fails to

e

+1 = −

⇒ 0 () = 65 − 43 + 92 − 2 ⇒

00 () = 304 − 122 + 18. To ﬁnd the critical numbers of , we’ll ﬁnd the

Fo

zeros of 0 . From the graph of 0 , it appears there are zeros at approximately

= −13, −04, and 05. Try 1 = −13 ⇒

2 = 1 −

0 (1 )

≈ −1293344 ⇒ 3 ≈ −1293227 ≈ 4 .

00 (1 )

ot

Now try 1 = −04 ⇒ 2 ≈ −0443755 ⇒ 3 ≈ −0441735 ⇒ 4 ≈ −0441731 ≈ 5 . Finally try

1 = 05 ⇒ 2 ≈ 0507937 ⇒ 3 ≈ 0507854 ≈ 4 . Therefore, = −1293227, −0441731, and 0507854 are

N

all the critical numbers correct to six decimal places.

(b) There are two critical numbers where 0 changes from negative to positive, so changes from decreasing to increasing.

(−1293227) ≈ −20212 and (0507854) ≈ −06721, so −20212 is the absolute minimum value of correct to four decimal places.

35.

= 2 sin ⇒ 0 = 2 cos + (sin )(2) ⇒

00 = 2 (− sin ) + (cos )(2) + (sin )(2) + 2 cos

= −2 sin + 4 cos + 2 sin

⇒

000 = −2 cos + (sin )(−2) + 4(− sin ) + (cos )(4) + 2 cos

= −2 cos − 6 sin + 6 cos .

From the graph of = 2 sin , we see that = 15 is a reasonable guess for the -coordinate of the inﬂection point. Using c ° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

SECTION 3.9

ANTIDERIVATIVES

¤

167

Newton’s method with () = 00 and 0 () = 000 , we get 1 = 15 ⇒ 2 ≈ 1520092, 3 ≈ 1519855 ≈ 4 .

The inﬂection point is about (1519855 2306964).

37. We need to minimize the distance from (0 0) to an arbitrary point ( ) on the

curve = ( − 1)2 . = 2 + 2 ⇒

() = 2 + [( − 1)2 ]2 = 2 + ( − 1)4 . When 0 = 0, will be

minimized and equivalently, = 2 will be minimized, so we will use Newton’s

method with = 0 and 0 = 00 .

() = 2 + 4( − 1)3

⇒ 0 () = 2 + 12( − 1)2 , so +1 = −

2 + 4( − 1)3

. Try 1 = 05 ⇒

2 + 12( − 1)2

2 = 04, 3 ≈ 0410127, 4 ≈ 0410245 ≈ 5 . Now (0410245) ≈ 0537841 is the minimum distance and the point on

e

the parabola is (0410245 0347810), correct to six decimal places.

375

[1 − (1 + )−60 ] ⇔ 48 = 1 − (1 + )−60

[multiply each term by (1 + )60 ] ⇔

rS

18,000 =

[1 − (1 + )− ] becomes

al

39. In this case, = 18,000, = 375, and = 5(12) = 60. So the formula =

48(1 + )60 − (1 + )60 + 1 = 0. Let the LHS be called (), so that

0 () = 48(60)(1 + )59 + 48(1 + )60 − 60(1 + )59

+1 = −

Fo

= 12(1 + )59 [4(60) + 4(1 + ) − 5] = 12(1 + )59 (244 − 1)

48 (1 + )60 − (1 + )60 + 1

. An interest rate of 1% per month seems like a reasonable estimate for

12(1 + )59 (244 − 1)

ot

= . So let 1 = 1% = 001, and we get 2 ≈ 00082202, 3 ≈ 00076802, 4 ≈ 00076291, 5 ≈ 00076286 ≈ 6 .

N

Thus, the dealer is charging a monthly interest rate of 076286% (or 955% per year, compounded monthly).

3.9 Antiderivatives

1. () = − 3 = 1 − 3

⇒ () =

1+1

− 3 + = 1 2 − 3 +

2

1+1

Check: 0 () = 1 (2) − 3 + 0 = − 3 = ()

2

3. () =

1

2

+ 3 2 − 4 3

4

5

Check: 0 () =

1

2

⇒ () = 1 +

2

+ 1 (32 ) − 1 (43 ) + 0 =

4

5

5. () = ( + 1)(2 − 1) = 22 + − 1

7. () = 725 + 8−45

9. () =

3 2+1

4 3+1

−

+ = 1 + 1 3 − 1 4 +

2

4

5

4 2+1

5 3+1

1

2

+ 3 2 − 4 3 = ()

4

5

⇒ () = 2

1

3

3 + 1 2 − + = 2 3 + 1 2 − +

2

3

2

⇒ () = 7 5 75 + 8(515 ) + = 575 + 4015 +

7

√

√

2 is a constant function, so () = 2 + .

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

¤

168

CHAPTER 3

APPLICATIONS OF DIFFERENTIATION

5

10−8

+ 1 = − 8 + 1

10

−8

4

−9

11. () = 9 = 10 has domain (−∞ 0) ∪ (0 ∞), so () =

5

−

+ 2

48

if 0 if 0

See Example 1(c) for a similar problem.

13. () =

1 + + 2

√

= −12 + 12 + 32

15. () = 2 sin − sec2

⇒ () = 212 + 2 32 + 2 52 +

3

5

⇒ () = −2 cos − tan + on the interval − + .

2

2

and − + for integers ≥ 1. The antiderivative is

2

2

() = 2 sec + 12 + 0 on the interval 0 or () = 2 sec + 12 + on the interval − + for

2

2

2

17. () = 2 sec tan + 1 −12 has domain 0

2

2

⇒ () = 5 ·

(0) = 4 ⇒ 05 −

1

3

5

6

−2·

+ = 5 − 1 6 + .

3

5

6

· 06 + = 4

⇒

= 4, so () = 5 − 1 6 + 4.

3

al

19. () = 54 − 25

e

integers ≥ 1.

The graph conﬁrms our answer since () = 0 when has a local maximum, is

rS

positive when is increasing, and is negative when is decreasing.

3

2

4

− 12

+6

+ = 54 − 43 + 32 +

21. () = 20 − 12 + 6 ⇒ () = 20

4

3

2

4

3

5

−4

+3

+ + = 5 − 4 + 3 + +

() = 5

5

4

3

23. 00 () =

0

2

⇒ 0 () =

2 23

3

25. 000 () = cos

2

3

Fo

3

53

53

⇒ 00 () = sin + 1

+ = 2 53 +

5

⇒ () =

⇒ 0 () = − cos + 1 +

2

5

83

83

+ + =

3 83

20

⇒

+ +

⇒ () = − sin + 2 + + ,

N

where = 1 1 .

2

√

ot

00

27. 0 () = 1 + 3

⇒ () = + 3 2 32 + = + 232 + . (4) = 4 + 2(8) + and (4) = 25 ⇒

3

20 + = 25 ⇒ = 5, so () = + 232 + 5.

29. 0 () =

√

(6 + 5) = 612 + 532

⇒ () = 432 + 252 + .

(1) = 6 + and (1) = 10 ⇒ = 4, so () = 432 + 252 + 4.

⇒ () = 2 sin + tan + because −2 2.

√

√

√

√

√

= 2 32 + 3 + = 2 3 + and = 4 ⇒ = 4 − 2 3, so () = 2 sin + tan + 4 − 2 3.

3

31. 0 () = 2 cos + sec2

3

33. 00 () = −2 + 12 − 122

⇒ 0 () = −2 + 62 − 43 + . 0 (0) = and 0 (0) = 12 ⇒ = 12, so

0 () = −2 + 62 − 43 + 12 and hence, () = −2 + 23 − 4 + 12 + . (0) = and (0) = 4 ⇒ = 4, so () = −2 + 23 − 4 + 12 + 4. c ° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

SECTION 3.9

35. 00 () = sin + cos

ANTIDERIVATIVES

¤

169

⇒ 0 () = − cos + sin + . 0 (0) = −1 + and 0 (0) = 4 ⇒ = 5, so

0 () = − cos + sin + 5 and hence, () = − sin − cos + 5 + . (0) = −1 + and (0) = 3 ⇒ = 4, so () = − sin − cos + 5 + 4.

37. 00 () = 4 + 6 + 242

⇒ 0 () = 4 + 32 + 83 +

⇒ () = 22 + 3 + 24 + + . (0) = and

(0) = 3 ⇒ = 3, so () = 22 + 3 + 24 + + 3. (1) = 8 + and (1) = 10 ⇒ = 2, so () = 22 + 3 + 24 + 2 + 3.

39. 00 () = 2 + cos

⇒ 0 () = 2 + sin + ⇒ () = 2 − cos + + .

= − 2 4 ⇒

(0) = −1 + and (0) = −1 ⇒ = 0. = 2 4 + and = 0 ⇒

2

2

2

2

= − , so () = 2 − cos − .

2

2

⇒

12 + 1 + = 6 ⇒

al

= 4. Therefore, () = 2 + + 4 and (2) = 22 + 2 + 4 = 10.

e

41. Given 0 () = 2 + 1, we have () = 2 + + . Since passes through (1 6), (1) = 6

rS

43. is the antiderivative of . For small , is negative, so the graph of its antiderivative must be decreasing. But both and

are increasing for small , so only can be ’s antiderivative. Also, is positive where is increasing, which supports our conclusion. The graph of must start at (0 1). Where the given graph, = (), has a

Fo

45.

local minimum or maximum, the graph of will have an inﬂection point.

Where is negative (positive), is decreasing (increasing).

Where changes from positive to negative, will have a maximum.

Where is decreasing (increasing), is concave downward (upward).

N

ot

Where changes from negative to positive, will have a minimum.

47.

2

0

() = 1

−1

if 0 ≤ 1 if 1 2 if 2 ≤ 3

2 +

⇒ () = +

− +

if 0 ≤ 1

if 1 2 if 2 ≤ 3

(0) = −1 ⇒ 2(0) + = −1 ⇒ = −1. Starting at the point

(0 −1) and moving to the right on a line with slope 2 gets us to the point (1 1).

The slope for 1 2 is 1, so we get to the point (2 2). Here we have used the fact that is continuous. We can include the point = 1 on either the ﬁrst or the second part of . The line connecting (1 1) to (2 2) is = , so = 0. The slope for

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

170

¤

CHAPTER 3

APPLICATIONS OF DIFFERENTIATION

2 ≤ 3 is −1, so we get to (3 1).

(3) = 1 ⇒ −3 + = 1 ⇒ = 4. Thus

2 − 1 if 0 ≤ ≤ 1

if 1 2

() =

− + 4 if 2 ≤ ≤ 3

Note that 0 () does not exist at = 1 or at = 2.

49. () =

sin

, −2 ≤ ≤ 2

1 + 2

Note that the graph of is one of an odd function, so the graph of will

51. () = 0 () = sin − cos

rS

al

e

be one of an even function.

⇒ () = − cos − sin + . (0) = −1 + and (0) = 0 ⇒ = 1, so

() = − cos − sin + 1.

⇒ () = 2 + + . (0) = and (0) = −2 ⇒ = −2, so () = 2 + − 2 and

Fo

53. () = 0 () = 2 + 1

() = 1 3 + 1 2 − 2 + . (0) = and (0) = 3 ⇒ = 3, so () = 1 3 + 1 2 − 2 + 3.

3

2

3

2

55. () = 0 () = 10 sin + 3 cos

⇒ () = −10 cos + 3 sin +

⇒ () = −10 sin − 3 cos + + .

6

.

Thus,

ot

(0) = −3 + = 0 and (2) = −3 + 2 + = 12 ⇒ = 3 and =

() = −10 sin − 3 cos +

6

+ 3.

N

57. (a) We ﬁrst observe that since the stone is dropped 450 m above the ground, (0) = 0 and (0) = 450.

0 () = () = −98 ⇒ () = −98 + . Now (0) = 0 ⇒ = 0, so () = −98 ⇒

() = −492 + . Last, (0) = 450 ⇒ = 450 ⇒ () = 450 − 492 .

(b) The stone reaches the ground when () = 0. 450 − 492 = 0 ⇒ 2 = 45049 ⇒ 1 =

(c) The velocity with which the stone strikes the ground is (1 ) = −98 45049 ≈ −939 ms.

45049 ≈ 958 s.

(d) This is just reworking parts (a) and (b) with (0) = −5. Using () = −98 + , (0) = −5 ⇒ 0 + = −5 ⇒

() = −98 − 5. So () = −492 − 5 + and (0) = 450 ⇒ = 450 ⇒ () = −492 − 5 + 450.

√

Solving () = 0 by using the quadratic formula gives us = 5 ± 8845 (−98) ⇒ 1 ≈ 909 s.

59. By Exercise 58 with = −98, () = −492 + 0 + 0 and () = 0 () = −98 + 0 . So

2

2

2

[()]2 = (−98 + 0 )2 = (98)2 2 − 1960 + 0 = 0 + 96042 − 1960 = 0 − 196 −492 + 0 .

2

But −492 + 0 is just () without the 0 term; that is, () − 0 . Thus, [()]2 = 0 − 196 [() − 0 ].

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

SECTION 3.9

ANTIDERIVATIVES

¤

171

61. Using Exercise 58 with = −32, 0 = 0, and 0 = (the height of the cliff ), we know that the height at time is

() = −162 + . () = 0 () = −32 and () = −120 ⇒ −32 = −120 ⇒ = 375, so

0 = (375) = −16(375)2 + ⇒ = 16(375)2 = 225 ft.

63. Marginal cost = 192 − 0002 = 0 ()

⇒ () = 192 − 00012 + . But (1) = 192 − 0001 + = 562 ⇒

= 560081. Therefore, () = 192 − 00012 + 560081 ⇒ (100) = 742081, so the cost of producing

100 items is $74208.

65. Taking the upward direction to be positive we have that for 0 ≤ ≤ 10 (using the subscript 1 to refer to 0 ≤ ≤ 10),

0

1 () = − (9 − 09) = 1 () ⇒ 1 () = −9 + 0452 + 0 , but 1 (0) = 0 = −10 ⇒

1 () = −9 + 0452 − 10 = 0 () ⇒ 1 () = − 9 2 + 0153 − 10 + 0 . But 1 (0) = 500 = 0

1

2

⇒

e

1 () = − 9 2 + 0153 − 10 + 500. 1 (10) = −450 + 150 − 100 + 500 = 100, so it takes

2

more than 10 seconds for the raindrop to fall. Now for 10, () = 0 = 0 () ⇒

al

() = constant = 1 (10) = −9(10) + 045(10)2 − 10 = −55 ⇒ () = −55.

rS

At 55 ms, it will take 10055 ≈ 18 s to fall the last 100 m. Hence, the total time is 10 +

67. () = , the initial velocity is 30 mih = 30 ·

50 mih = 50 ·

5280

3600

=

220

3

5280

3600

100

55

=

130

11

≈ 118 s.

= 44 fts, and the ﬁnal velocity (after 5 seconds) is

fts. So () = + and (0) = 44 ⇒ = 44. Thus, () = + 44 ⇒

220

,

3

so 5 + 44 =

220

3

⇒

5 =

88

3

⇒

=

88

15

≈ 587 fts2 .

Fo

(5) = 5 + 44. But (5) =

69. Let the acceleration be () = kmh2 . We have (0) = 100 kmh and we can take the initial position (0) to be 0.

We want the time for which () = 0 to satisfy () 008 km. In general, 0 () = () = , so () = + , where = (0) = 100. Now 0 () = () = + 100, so () = 1 2 + 100 + , where = (0) = 0.

2

−

2

1

100

1

5,000

1

100

−

= 10,000

−

=−

. The condition ( ) must satisfy is

+ 100 −

2

2

N

( ) =

ot

Thus, () = 1 2 + 100. Since ( ) = 0, we have + 100 = 0 or = −100, so

2

5,000

5,000

008 ⇒ −

008

[ is negative] ⇒ −62,500 kmh2 , or equivalently,

− 3125 ≈ −482 ms2 .

648

71. (a) First note that 90 mih = 90 ×

5280

3600

= 0. Now 4 = 132 when =

fts = 132 fts. Then () = 4 fts2

132

4

⇒ () = 4 + , but (0) = 0 ⇒

= 33 s, so it takes 33 s to reach 132 fts. Therefore, taking (0) = 0, we have

() = 22 , 0 ≤ ≤ 33. So (33) = 2178 ft. 15 minutes = 15(60) = 900 s, so for 33 ≤ 933 we have

() = 132 fts ⇒ (933) = 132(900) + 2178 = 120,978 ft = 229125 mi.

(b) As in part (a), the train accelerates for 33 s and travels 2178 ft while doing so. Similarly, it decelerates for 33 s and travels

2178 ft at the end of its trip. During the remaining 900 − 66 = 834 s it travels at 132 fts, so the distance traveled is

132 · 834 = 110,088 ft. Thus, the total distance is 2178 + 110,088 + 2178 = 114,444 ft = 21675 mi. c ° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

172

¤

CHAPTER 3 APPLICATIONS OF DIFFERENTIATION

(c) 45 mi = 45(5280) = 237,600 ft. Subtract 2(2178) to take care of the speeding up and slowing down, and we have

233,244 ft at 132 fts for a trip of 233,244132 = 1767 s at 90 mih. The total time is

1767 + 2(33) = 1833 s = 30 min 33 s = 3055 min.

(d) 375(60) = 2250 s. 2250 − 2(33) = 2184 s at maximum speed. 2184(132) + 2(2178) = 292,644 total feet or

292,6445280 = 55425 mi.

3 Review

1. A function has an absolute maximum at = if () is the largest function value on the entire domain of , whereas has

a local maximum at if () is the largest function value when is near . See Figure 6 in Section 3.1.

e

2. (a) See the Extreme Value Theorem on page 199.

al

(b) See the Closed Interval Method on page 202.

(b) See the deﬁnition of a critical number on page 201.

4. (a) See Rolle’s Theorem on page 208.

rS

3. (a) See Fermat’s Theorem on page 200.

(b) See the Mean Value Theorem on page 209. Geometric interpretation—there is some point on the graph of a function

Fo

[on the interval ( )] where the tangent line is parallel to the secant line that connects ( ()) and ( ()).

5. (a) See the Increasing/Decreasing (I/D) Test on page 214.

(b) If the graph of lies above all of its tangents on an interval , then it is called concave upward on .

ot

(c) See the Concavity Test on page 217.

(d) An inﬂection point is a point where a curve changes its direction of concavity. They can be found by determining the points

N

at which the second derivative changes sign.

6. (a) See the First Derivative Test on page 215.

(b) See the Second Derivative Test on page 218.

(c) See the note before Example 7 in Section 3.3.

7. (a) See Deﬁnitions 3.4.1 and 3.4.5.

(b) See Deﬁnitions 3.4.2 and 3.4.6.

(c) See Deﬁnition 3.4.7.

(d) See Deﬁnition 3.4.3.

8. Without calculus you could get misleading graphs that fail to show the most interesting features of a function.

See Example 1 in Section 3.6.

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

CHAPTER 3 REVIEW

¤

173

9. (a) See Figure 2 in Section 3.8.

(b) 2 = 1 −

(1 )

0 (1 )

(c) +1 = −

( )

0 ( )

(d) Newton’s method is likely to fail or to work very slowly when 0 (1 ) is close to 0. It also fails when 0 ( ) is undeﬁned, such as with () = 1 − 2 and 1 = 1.

10. (a) See the deﬁnition at the beginning of Section 3.9.

1. False.

e

(b) If 1 and 2 are both antiderivatives of on an interval , then they differ by a constant.

For example, take () = 3 , then 0 () = 32 and 0 (0) = 0, but (0) = 0 is not a maximum or minimum;

For example, () = is continuous on (0 1) but attains neither a maximum nor a minimum value on (0 1).

rS

3. False.

al

(0 0) is an inﬂection point.

Don’t confuse this with being continuous on the closed interval [ ], which would make the statement true.

This is an example of part (b) of the I/D Test.

7. False.

0 () = 0 () ⇒ () = () + . For example, if () = + 2 and () = + 1, then 0 () = 0 () = 1, but () 6= ().

The graph of one such function is sketched.

11. True.

N

ot

9. True.

Fo

5. True.

Let 1 2 where 1 2 ∈ . Then (1 ) (2 ) and (1 ) (2 ) [since and are increasing on ],

so ( + )(1 ) = (1 ) + (1 ) (2 ) + (2 ) = ( + )(2 ).

13. False.

Take () = and () = − 1. Then both and are increasing on (0 1). But () () = ( − 1) is not increasing on (0 1).

15. True.

Let 1 2 ∈ and 1 2 . Then (1 ) (2 ) [ is increasing] ⇒

1

1

[ is positive] ⇒

(1 )

(2 )

(1 ) (2 ) ⇒ () = 1 () is decreasing on .

17. True.

If is periodic, then there is a number such that ( + ) = () for all . Differentiating gives

0 () = 0 ( + ) · ( + )0 = 0 ( + ) · 1 = 0 ( + ), so 0 is periodic. c ° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

¤

174

CHAPTER 3 APPLICATIONS OF DIFFERENTIATION

By the Mean Value Theorem, there exists a number in (0 1) such that (1) − (0) = 0 ()(1 − 0) = 0 ().

19. True.

Since 0 () is nonzero, (1) − (0) 6= 0, so (1) 6= (0).

1. () = 3 − 62 + 9 + 1, [2 4].

0 () = 32 − 12 + 9 = 3(2 − 4 + 3) = 3( − 1)( − 3). 0 () = 0 ⇒

= 1 or = 3, but 1 is not in the interval. 0 () 0 for 3 4 and 0 () 0 for 2 3, so (3) = 1 is a local minimum value. Checking the endpoints, we ﬁnd (2) = 3 and (4) = 5. Thus, (3) = 1 is the absolute minimum value and

(4) = 5 is the absolute maximum value.

3. () =

3 − 4

(2 + 1)(3) − (3 − 4)(2)

−(32 − 8 − 3)

−(3 + 1)( − 3)

=

=

.

, [−2 2]. 0 () =

2 +1

2 + 1)2

(

(2 + 1)2

(2 + 1)2

al

e

0 () = 0 ⇒ = − 1 or = 3, but 3 is not in the interval. 0 () 0 for − 1 2 and 0 () 0 for

3

3

1

1

−5

9

−2 − 3 , so − 3 = 109 = − 2 is a local minimum value. Checking the endpoints, we ﬁnd (−2) = −2 and

5. () = + 2 cos , [− ].

6

=

5

6

−

6

+

1

2

⇒ =

5

, 6.

6

0 () 0 for

√

3 ≈ 226 is a local maximum value and

√

3 ≈ 089 is a local minimum value. Checking the endpoints, we ﬁnd (−) = − − 2 ≈ −514 and

Fo

5

is the absolute maximum value.

0 () = 1 − 2 sin . 0 () = 0 ⇒ sin =

− and 5 , and 0 () 0 for 5 , so =

6

6

6

6

6

2

5

rS

(2) = 2 . Thus, − 1 = − 9 is the absolute minimum value and (2) =

5

3

2

() = − 2 ≈ 114. Thus, (−) = − − 2 is the absolute minimum value and maximum value.

6

=

6

+

√

3 is the absolute

5

4 = 3 + 0 + 0 = 1

1

6−0+0

2

4

ot

1

3+ 3 −

34 + − 5

= lim

7. lim

2

→∞ 64 − 22 + 1

→∞

6− 2 +

lim

→−∞

√

√

√

4 + 12

42 + 1 2

42 + 1

√

= lim

= lim

→−∞ (3 − 1) 2

→−∞ −3 + 1

3 − 1

N

9.

=

11. lim

→∞

[since − = || =

√

2 for 0]

2

2

=−

−3 + 0

3

√

√

42 + 3 − 2

42 + 3 + 2

(42 + 3) − 42

·√

= lim √

2 + 3 + 2

→∞

→∞

1

4

42 + 3 + 2

√

3

3 2

= lim √

= lim √

√

→∞

42 + 3 + 2 →∞

42 + 3 + 2 2

√

42 + 3 − 2 = lim

3

= lim

→∞

4 + 3 + 2

=

[since = || =

√

2 for 0]

3

3

=

2+2

4

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

CHAPTER 3 REVIEW

¤

13. (0) = 0, 0 (−2) = 0 (1) = 0 (9) = 0, lim () = 0, lim () = −∞,

→∞

→6

0 () 0 on (−∞ −2), (1 6), and (9 ∞), 0 () 0 on (−2 1) and (6 9),

00 () 0 on (−∞ 0) and (12 ∞), 00 () 0 on (0 6) and (6 12)

15. is odd, 0 () 0 for 0 2,

17. = () = 2 − 2 − 3

00 () 0 for 3, lim→∞ () = −2

A. = R B. -intercept: (0) = 2.

H.

e

00 () 0 for 0 3,

0 () 0 for 2,

al

The -intercept (approximately 0770917) can be found using Newton’s

Method. C. No symmetry D. No asymptote

rS

E. 0 () = −2 − 32 = −(32 + 2) 0, so is decreasing on R.

F. No extreme value G. 00 () = −6 0 on (0 ∞) and 00 () 0 on

(−∞ 0), so is CD on (0 ∞) and CU on (−∞ 0). There is an IP at (0 2).

A. = R B. -intercept: (0) = 0; -intercepts: () = 0 ⇔

Fo

19. = () = 4 − 33 + 32 − = ( − 1)3

= 0 or = 1 C. No symmetry D. is a polynomial function and hence, it has no asymptote.

N

ot

E. 0 () = 43 − 92 + 6 − 1. Since the sum of the coefﬁcients is 0, 1 is a root of 0 , so

0 () = ( − 1) 42 − 5 + 1 = ( − 1)2 (4 − 1). 0 () 0 ⇒ 1 , so is decreasing on −∞ 1

4

4

H.

and is increasing on 1 ∞ . F. 0 () does not change sign at = 1, so

4

1

27

there is not a local extremum there. 4 = − 256 is a local minimum value.

G. 00 () = 122 − 18 + 6 = 6(2 − 1)( − 1). 00 () = 0 ⇔ =

or 1. 00 () 0 ⇔ 1 1 ⇒ is CD on 1 1 and CU on

2

2

1

−∞ 1 and (1 ∞). There are inﬂection points at 1 − 16 and (1 0).

2

2

21. = () =

D.

lim

→±∞

1

( − 3)2

1

2

A. = { | 6= 0 3} = (−∞ 0) ∪ (0 3) ∪ (3 ∞) B. No intercepts. C. No symmetry.

1

= 0, so = 0 is a HA.

( − 3)2

so = 0 and = 3 are VA. E. 0 () = −

lim

→0+

1

1

1

= ∞, lim

= −∞, lim

= ∞,

2

→3 ( − 3)2

( − 3)2

→0− ( − 3)

( − 3)2 + 2( − 3)

3(1 − )

= 2

2 ( − 3)4

( − 3)3

⇒ 0 () 0 ⇔ 1 3,

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

175

176

¤

CHAPTER 3 APPLICATIONS OF DIFFERENTIATION

so is increasing on (1 3) and decreasing on (−∞ 0), (0 1), and (3 ∞).

F. Local minimum value (1) =

1

4

G. 00 () =

H.

6(22 − 4 + 3)

.

3 ( − 3)4

Note that 22 − 4 + 3 0 for all since it has negative discriminant.

So 00 () 0 ⇔ 0 ⇒ is CU on (0 3) and (3 ∞) and

CD on (−∞ 0). No IP

23. = () =

→∞

lim

→−8+

A. = { | 6= −8} B. Intercepts are 0 C. No symmetry

2

64

= ∞, but () − ( − 8) =

→ 0 as → ∞, so = − 8 is a slant asymptote.

+8

+8

64

( + 16)

2

2

=

0 ⇔

= ∞ and lim

= −∞, so = −8 is a VA. E. 0 () = 1 −

+8

( + 8)2

( + 8)2

→−8− + 8

e

D. lim

2

64

= −8+

+8

+8

H.

0 or −16, so is increasing on (−∞ −16) and (0 ∞) and

al

decreasing on (−16 −8) and (−8 0)

F. Local maximum value (−16) = −32, local minimum value (0) = 0

rS

G. 00 () = 128( + 8)3 0 ⇔ −8, so is CU on (−8 ∞) and

CD on (−∞ −8). No IP

√

2 + A. = [−2 ∞) B. -intercept: (0) = 0; -intercepts: −2 and 0 C. No symmetry

Fo

25. = () =

√

3 + 4

1

√

+ 2+= √

[ + 2(2 + )] = √

= 0 when = − 4 , so is

3

2 2+

2 2+

2 2+

√

decreasing on −2 − 4 and increasing on − 4 ∞ . F. Local minimum value − 4 = − 4 2 = − 4 9 6 ≈ −109,

3

3

3

3

3

no local maximum

ot

D. No asymptote E. 0 () =

H.

=

N

√

1

2 2 + · 3 − (3 + 4) √

6(2 + ) − (3 + 4)

2+

=

G. 00 () =

4(2 + )

4(2 + )32

3 + 8

4(2 + )32

00 () 0 for −2, so is CU on (−2 ∞). No IP

27. = () = sin2 − 2 cos

A. = R B. -intercept: (0) = −2 C. (−) = (), so is symmetric with respect

to the -axis. has period 2. D. No asymptote E. 0 = 2 sin cos + 2 sin = 2 sin (cos + 1). 0 = 0 ⇔ sin = 0 or cos = −1 ⇔ = or = (2 + 1). 0 0 when sin 0, since cos + 1 ≥ 0 for all .

Therefore, 0 0 [and so is increasing] on (2 (2 + 1)); 0 0 [and so is decreasing] on ((2 − 1) 2).

F. Local maximum values are ((2 + 1)) = 2; local minimum values are (2) = −2.

G. 0 = sin 2 + 2 sin ⇒

00 = 2 cos 2 + 2 cos = 2(2 cos2 − 1) + 2 cos = 4 cos2 + 2 cos − 2

= 2(2 cos2 + cos − 1) = 2(2 cos − 1)(cos + 1)

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

CHAPTER 3 REVIEW

00 = 0 ⇔ cos =

¤

177

H. or −1 ⇔ = 2 ± or = (2 + 1).

3

00

00 0 [and so is CU] on 2 − 2 + ; ≤ 0 [and so is CD]

3

3

5 on 2 + 3 2 + 3 . There are inﬂection points at 2 ± − 1 .

3

4

1

2

3 (2) − 2 − 1 32

3 − 2

⇒ () =

=

6

4

3

4

2

2

(−2) − 3 − 4

2 − 12

=

00 () =

8

5

2 − 1

29. () =

3

0

⇒

Estimates: From the graphs of 0 and 00 , it appears that is increasing on

(−173 0) and (0 173) and decreasing on (−∞ −173) and (173 ∞);

(−17) = −038; is CU on (−245 0) and (245 ∞), and CD on

(−∞ −245) and (0 245); and has inﬂection points at about

al

(−245 −034) and (245 034).

e

has a local maximum of about (173) = 038 and a local minimum of about

3 − 2 is positive for 0 2 3, that is, is increasing

4

√

√ on − 3 0 and 0 3 ; and 0 () is negative (and so is decreasing) on

√

√

√

−∞ − 3 and

3 ∞ . 0 () = 0 when = ± 3.

√

0 goes from positive to negative at = 3, so has a local maximum of

√ (√3 )2 − 1

3 = √ 3 =

( 3)

√

2 3

;

9

Fo

rS

Exact: Now 0 () =

and since is odd, we know that maxima on the

interval (0 ∞) correspond to minima on (−∞ 0), so has a local minimum of

N

ot

√

√

22 − 12 is positive (so is CU) on

− 3 = − 2 9 3 . Also, 00 () =

5

√

√

√

6 ∞ , and negative (so is CD) on −∞ − 6 and

− 6 0 and

√

√ √

√

√

0 6 . There are IP at

6 5366 and − 6 − 5366 .

31. () = 36 − 55 + 4 − 53 − 22 + 2

⇒ 0 () = 185 − 254 + 43 − 152 − 4 ⇒

00 () = 904 − 1003 + 122 − 30 − 4

From the graphs of 0 and 00 , it appears that is increasing on (−023 0) and (162 ∞) and decreasing on (−∞ −023) and (0 162); has a local maximum of (0) = 2 and local minima of about (−023) = 196 and (162) = −192; c ° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

178

¤

CHAPTER 3 APPLICATIONS OF DIFFERENTIATION

is CU on (−∞ −012) and (124 ∞) and CD on (−012 124); and has inﬂection points at about (−012 198) and

(124 −121).

33. Let () = 3 + 2 cos + 5. Then (0) = 7 0 and (−) = −3 − 2 + 5 = −3 + 3 = −3( − 1) 0 and since is

continuous on R (hence on [− 0]), the Intermediate Value Theorem assures us that there is at least one zero of in [− 0].

Now 0 () = 3 − 2 sin 0 implies that is increasing on R, so there is exactly one zero of , and hence, exactly one real

e

root of the equation 3 + 2 cos + 5 = 0.

√

√

5

√

33 − 5 32

= 5 33 − 2, but 1 −45 0 ⇒

5

33 − 32

rS

(32 33) such that 0 () = 1 −45 =

5

al

35. Since is continuous on [32 33] and differentiable on (32 33), then by the Mean Value Theorem there exists a number in

√

5

33 − 2 0 ⇒

0 is decreasing, so that 0 () 0 (32) = 1 (32)−45 = 00125 ⇒ 00125 0 () =

5

√

5

33 20125.

37. (a) () = (2 )

√

5

33 20125.

⇒ 0 () = 2 0 (2 ) by the Chain Rule. Since 0 () 0 for all 6= 0, we must have 0 (2 ) 0 for

Fo

Therefore, 2

√

5

33 − 2 ⇒

√

5

33 2. Also

6= 0, so 0 () = 0 ⇔ = 0. Now 0 () changes sign (from negative to positive) at = 0, since one of its factors,

0 (2 ), is positive for all , and its other factor, 2, changes from negative to positive at this point, so by the First

ot

Derivative Test, has a local and absolute minimum at = 0.

(b) 0 () = 2 0 (2 ) ⇒ 00 () = 2[ 00 (2 )(2) + 0 (2 )] = 42 00 (2 ) + 2 0 (2 ) by the Product Rule and the Chain

N

Rule. But 2 0 for all 6= 0, 00 (2 ) 0 [since is CU for 0], and 0 (2 ) 0 for all 6= 0, so since all of its factors are positive, 00 () 0 for 6= 0. Whether 00 (0) is positive or 0 doesn’t matter [since the sign of 00 does not change there]; is concave upward on R.

1 + = |1 + 1 + | , so assume

√

39. If = 0, the line is vertical and the distance from = − to (1 1 ) is

2 + 2

6= 0. The square of the distance from (1 1 ) to the line is () = ( − 1 )2 + ( − 1 )2 where + + = 0, so

2

we minimize () = ( − 1 )2 + − −

− 1

− 1

.

⇒ 0 () = 2 ( − 1 ) + 2 − −

−

2 1 − 1 −

2

00 and this gives a minimum since () = 2 1 + 2 0. Substituting

() = 0 ⇒ =

2 + 2

0

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

CHAPTER 3 REVIEW

¤

179

(1 + 1 + )2

, so the minimum distance is

2 + 2

this value of into () and simplifying gives () =

|1 + 1 + |

√

() =

.

2 + 2

By similar triangles,

41.

, so the area of the triangle is

= √

2 − 2

2

⇒

() = 1 (2) = = √

2

2 − 2

√

√

2 ( − 3)

2 2 − 2 − 2 ( − ) 2 − 2

0 () =

=

=0

2 − 2

(2 − 2)32 when = 3

e

√

(92 )

0 () 0 when 2 3, 0 () 0 when 3. So = 3 gives a minimum and (3) = √

= 3 3 2 .

3

√

We minimize () = | | + | | + | | = 2 2 + 16 + (5 − ),

√

√

0 ≤ ≤ 5. 0 () = 2 2 + 16 − 1 = 0 ⇔ 2 = 2 + 16 ⇔

4

4

42 = 2 + 16 ⇔ = √3 . (0) = 13, √3 ≈ 119, (5) ≈ 128, so the

rS

al

43.

minimum occurs when =

+

⇒

=

2 () + ()

1

− 2

Fo

45. =

4

√

3

≈ 23.

=0 ⇔

1

= 2

⇔ 2 = 2

⇔ = .

This gives the minimum velocity since 0 0 for 0 and 0 0 for .

47. Let denote the number of $1 decreases in ticket price. Then the ticket price is $12 − $1(), and the average attendance is

ot

11,000 + 1000(). Now the revenue per game is

N

() = (price per person) × (number of people per game)

= (12 − )(11,000 + 1000) = −10002 + 1000 + 132,000

for 0 ≤ ≤ 4 [since the seating capacity is 15,000] ⇒ 0 () = −2000 + 1000 = 0 ⇔ = 05. This is a maximum since 00 () = −2000 0 for all . Now we must check the value of () = (12 − )(11,000 + 1000) at

= 05 and at the endpoints of the domain to see which value of gives the maximum value of .

(0) = (12)(11,000) = 132,000, (05) = (115)(11,500) = 132,250, and (4) = (8)(15,000) = 120,000. Thus, the maximum revenue of $132,250 per game occurs when the average attendance is 11,500 and the ticket price is $1150.

49. () = 5 − 4 + 32 − 3 − 2

⇒ 0 () = 54 − 43 + 6 − 3, so +1 = −

5 − 4 + 32 − 3 − 2

.

54 − 43 + 6 − 3

Now 1 = 1 ⇒ 2 = 15 ⇒ 3 ≈ 1343860 ⇒ 4 ≈ 1300320 ⇒ 5 ≈ 1297396 ⇒

6 ≈ 1297383 ≈ 7 , so the root in [1 2] is 1297383, to six decimal places.

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

180

¤

CHAPTER 3 APPLICATIONS OF DIFFERENTIATION

51. () = cos + − 2

⇒ 0 () = − sin + 1 − 2. 0 () exists for all

, so to ﬁnd the maximum of , we can examine the zeros of 0 .

From the graph of 0 , we see that a good choice for 1 is 1 = 03.

Use () = − sin + 1 − 2 and 0 () = − cos − 2 to obtain

2 ≈ 033535293, 3 ≈ 033541803 ≈ 4 . Since 00 () = − cos − 2 0 for all , (033541803) ≈ 116718557 is the absolute maximum.

53. 0 () =

√

√

3

3 + 2 = 32 + 23

55. 0 () = 2 − 3 sin

⇒ () =

52

53

+

+ = 2 52 + 3 53 +

5

5

52

53

⇒ () = 2 + 3 cos + .

(0) = 3 + and (0) = 5 ⇒ = 2, so () = 2 + 3 cos + 2.

⇒ 0 () = − 32 + 163 + . 0 (0) = and 0 (0) = 2 ⇒ = 2, so

al

0 () = − 32 + 163 + 2 and hence, () = 1 2 − 3 + 44 + 2 + .

2

e

57. 00 () = 1 − 6 + 482

(0) = and (0) = 1 ⇒ = 1, so () = 1 2 − 3 + 44 + 2 + 1.

2

⇒ () = 2 + cos + .

rS

59. () = 0 () = 2 − sin

(0) = 0 + 1 + = + 1 and (0) = 3 ⇒ + 1 = 3 ⇒ = 2, so () = 2 + cos + 2.

ot

Fo

61. () = 2 sin(2 ), 0 ≤ ≤

63. Choosing the positive direction to be upward, we have () = −98

⇒ () = −98 + 0 , but (0) = 0 = 0

⇒

N

() = −98 = 0 () ⇒ () = −492 + 0 , but (0) = 0 = 500 ⇒ () = −492 + 500. When = 0,

−492 + 500 = 0 ⇒ 1 = 500 ≈ 101 ⇒ (1 ) = −98 500 ≈ −98995 ms. Since the canister has been

49

49

designed to withstand an impact velocity of 100 ms, the canister will not burst.

65. (a)

The cross-sectional area of the rectangular beam is

√

= 2 · 2 = 4 = 4 100 − 2 , 0 ≤ ≤ 10, so

= 4 1 (100 − 2 )−12 (−2) + (100 − 2 )12 · 4

2

4[−2 + 100 − 2 ]

−42

2 12

=

+ 4(100 − )

=

.

(100 − 2 )12

(100 − 2 )12

= 0 when −2 + 100 − 2 = 0 ⇒

2 = 50 ⇒ =

√

√ 2 √

50 ≈ 707 ⇒ = 100 −

50 = 50.

Since (0) = (10) = 0, the rectangle of maximum area is a square.

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

CHAPTER 3 REVIEW

(b)

¤

The cross-sectional area of each rectangular plank (shaded in the ﬁgure) is

√

√

√

√

= 2 − 50 = 2 100 − 2 − 50 , 0 ≤ ≤ 50, so

√

√

= 2 100 − 2 − 50 + 2 1 (100 − 2 )−12 (−2)

2

= 2(100 − 2 )12 − 2

Set

√

50 −

22

(100 − 2 )12

√

√

= 0: (100 − 2 ) − 50 (100 − 2 )12 − 2 = 0 ⇒ 100 − 22 = 50 (100 − 2 )12

⇒

e

10,000 − 4002 + 44 = 50(100 − 2 ) ⇒ 44 − 3502 + 5000 = 0 ⇒ 24 − 1752 + 2500 = 0 ⇒

√

√

175 ± 10,625

2

=

≈ 6952 or 1798 ⇒ ≈ 834 or 424. But 834 50, so 1 ≈ 424 ⇒

4

√

√

− 50 = 100 − 2 − 50 ≈ 199. Each plank should have dimensions about 8 1 inches by 2 inches.

1

2

al

(c) From the ﬁgure in part (a), the width is 2 and the depth is 2, so the strength is

10

√ .

3

The dimensions should be

20

√

3

≈ 1155 inches by

√

20 2

√

3

≈ 1633 inches.

N

ot

Fo

maximum strength occurs when =

rS

= (2)(2)2 = 8 2 = 8(100 − 2 ) = 800 − 83 , 0 ≤ ≤ 10. = 800 − 242 = 0 when

√

√

10

√

242 = 800 ⇒ 2 = 100 ⇒ = √3 ⇒ = 200 = 10 3 2 = 2 . Since (0) = (10) = 0, the

3

3

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

181

N ot e

al

rS

Fo

PROBLEMS PLUS

1. Let () = sin − cos on [0 2] since has period 2. 0 () = cos + sin = 0

⇔ cos = − sin ⇔

√ tan = −1 ⇔ = 3 or 7 . Evaluating at its critical numbers and endpoints, we get (0) = −1, 3 = 2,

4

4

4

√

√

√

7

4 = − 2, and (2) = −1. So has absolute maximum value 2 and absolute minimum value − 2. Thus,

√

√

√

− 2 ≤ sin − cos ≤ 2 ⇒ |sin − cos | ≤ 2.

3. =

sin

⇒ 0 =

cos − sin

2

⇒ 00 =

−2 sin − 2 cos + 2 sin

. If ( ) is an inﬂection point,

3

then 00 = 0 ⇒ (2 − 2 ) sin = 2 cos ⇒ (2 − 2 )2 sin2 = 42 cos2 ⇒

⇒ (4 + 4)

sin2 sin

.

= 4 ⇒ 2 (4 + 4) = 4 since =

2

al

(4 + 4 ) sin2 = 42

e

(2 − 2 )2 sin2 = 42 (1 − sin2 ) ⇒ (4 − 42 + 4 ) sin2 = 42 − 42 sin2 ⇒

At a highest or lowest point,

rS

5. Differentiating 2 + + 2 = 12 implicitly with respect to gives 2 + +

2 +

+ 2

= 0, so

=−

.

+ 2

= 0 ⇔ = −2. Substituting −2 for in the original equation gives

Fo

2 + (−2) + (−2)2 = 12, so 32 = 12 and = ±2. If = 2, then = −2 = −4, and if = −2 then = 4. Thus, the highest and lowest points are (−2 4) and (2 −4).

1

1

+

1 + ||

1 + | − 2|

1

1 +

1 − 1 − ( − 2)

1

1

+

=

1 + 1 − ( − 2)

1

1

+

1 + 1 + ( − 2)

if 0

N

ot

7. () =

if 0 ≤ 2 if ≥ 2

⇒

1

1

(1 − )2 + (3 − )2

−1

1

0

+

() =

2

(3 − )2

(1 + )

−1

1

−

(1 + )2

( − 1)2

if 0 if 0 2 if 2

We see that 0 () 0 for 0 and 0 () 0 for 2. For 0 2, we have

0 () =

1

1

(2 + 2 + 1) − (2 − 6 + 9)

8 ( − 1)

−

=

=

, so 0 () 0 for 0 1,

2

2

(3 − )

( + 1)

(3 − )2 ( + 1)2

(3 − )2 ( + 1)2

0 (1) = 0 and 0 () 0 for 1 2. We have shown that 0 () 0 for 0; 0 () 0 for 0 1; 0 () 0 for

1 2; and 0 () 0 for 2. Therefore, by the First Derivative Test, the local maxima of are at = 0 and = 2, where takes the value 4 . Therefore,

3

4

3

is the absolute maximum value of .

9. = 1 2 and = 2 2 , where 1 and 2 are the solutions of the quadratic equation 2 = + . Let = 2

1

2

and set 1 = (1 0), 1 = (2 0), and 1 = ( 0). Let () denote the area of triangle . Then () can be expressed

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

183

184

¤

CHAPTER 3 PROBLEMS PLUS

in terms of the areas of three trapezoids as follows:

() = area (1 1 ) − area (1 1 ) − area (1 1 )

= 1 2 + 2 (2 − 1 ) − 1 2 + 2 ( − 1 ) − 1 2 + 2 (2 − )

1

2

1

2

2

2

2

After expanding and canceling terms, we get

() = 1 2 2 − 1 2 − 2 + 1 2 − 2 2 + 2 = 1 2 (2 − ) + 2 ( − 1 ) + 2 (1 − 2 )

1

2

1

2

1

2

2

2

0 () = 1 −2 + 2 + 2(1 − 2 ) . 00 () = 1 [2(1 − 2 )] = 1 − 2 0 since 2 1 .

1

2

2

2

0 () = 0 ⇒ 2(1 − 2 ) = 2 − 2

1

2

⇒ = 1 (1 + 2 ).

2

2 1

1 2 (2 − 1 ) + 2 1 (2 − 1 ) + 1 (1 + 2 )2 (1 − 2 )

2 2

4

= 1 1 (2 − 1 ) 2 + 2 − 1 (2 − 1 )(1 + 2 )2 = 1 (2 − 1 ) 2 2 + 2 − 2 + 21 2 + 2

1

2

1

2

1

2

2 2

4

8

= 1 (2 − 1 ) 2 − 21 2 + 2 = 1 (2 − 1 )(1 − 2 )2 = 1 (2 − 1 )(2 − 1 )2 = 1 (2 − 1 )3

1

2

8

8

8

8

1

2

e

( ) =

To put this in terms of and , we solve the system = 2 and = 1 + , giving us 2 − 1 − = 0 ⇒

1

1

al

√

√

√

3

− 2 + 4 . Similarly, 2 = 1 + 2 + 4 . The area is then 1 (2 − 1 )3 = 1 2 + 4 ,

2

8

8

and is attained at the point 2 = 1 1 2 .

2

4

1

2

rS

1 =

Note: Another way to get an expression for () is to use the formula for an area of a triangle in terms of the coordinates of

the vertices: () = 1 2 2 − 1 2 + 1 2 − 2 + 2 − 2 2 .

1

2

1

2

2

⇒ 0 () = − 2 + − 6 sin 2 (2) + ( − 2). The derivative exists

Fo

11. () = 2 + − 6 cos 2 + ( − 2) + cos 1

for all , so the only possible critical points will occur where 0 () = 0 ⇔ 2( − 2)( + 3) sin 2 = − 2 ⇔ either = 2 or 2( + 3) sin 2 = 1, with the latter implying that sin 2 =

ot

1

1

−1 or

1. Solving these inequalities, we get

2( + 3)

2( + 3)

N

this equation has no solution whenever either

−7 −5.

2

2

1

. Since the range of sin 2 is [−1 1],

2( + 3)

13. (a) Let = ||, = ||, and 1 = ||, so that || · || = 1. We compute

the area A of 4 in two ways.

First, A =

1

2

|| || sin 2 =

3

1

2

·1·

√

3

2

=

√

3

.

4

Second,

A = (area of 4) + (area of 4) =

= 1

2

√

3

2

+ 1 (1)

2

√

3

2

=

√

3

(

4

1

2

|| || sin +

3

1

2

|| || sin

3

+ 1)

Equating the two expressions for the area, we get

√

3

4

1

=

+

√

3

4

⇔ =

1

= 2

, 0.

+ 1

+1

Another method: Use the Law of Sines on the triangles and . In 4, we have

∠ + ∠ + ∠ = 180◦

⇔ 60◦ + + ∠ = 180◦

⇔ ∠ = 120◦ − . Thus,

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

CHAPTER 3 PROBLEMS PLUS

¤

185

√

√ cos + 1 sin

2

⇒

= 23 cot + 1 , and by a

2

sin

√

similar argument with 4, 23 cot = 2 + 1 . Eliminating cot gives = 2 + 1 + 1 ⇒

2

2

2

, 0.

= 2

+1

sin(120◦ − ) sin 120◦ cos − cos 120◦ sin

=

=

=

sin sin

3

2

(b) We differentiate our expression for with respect to to ﬁnd the maximum:

(2 + 1) − (2)

1 − 2

=

= 2

= 0 when = 1. This indicates a maximum by the First Derivative Test, since

(2 + 1)2

( + 1)2

0 () 0 for 0 1 and 0 () 0 for 1, so the maximum value of is (1) = 1 .

2

15. (a) =

1

2

with sin = , so = 1 sin . But is a constant,

2

al

e

so differentiating this equation with respect to , we get

1

=0=

cos

+

sin +

sin

⇒

2

1

1

cos

= − sin

+

⇒

= − tan

+

.

rS

(b) We use the Law of Cosines to get the length of side in terms of those of and , and then we differentiate implicitly with

Fo

respect to : 2 = 2 + 2 − 2 cos ⇒

= 2

+ 2

− 2 (− sin )

+

cos +

cos

⇒

2

1

=

+

+ sin

−

cos − cos . Now we substitute our value of from the Law of

Cosines and the value of from part (a), and simplify (primes signify differentiation by ):

0 + 0 + sin [− tan (0 + 0)] − (0 + 0 )(cos )

√

=

2 + 2 − 2 cos

ot

0 + 0 − [sin2 (0 + 0 ) + cos2 (0 + 0 )] cos

0 + 0 − (0 + 0 ) sec

√

√

=

2 + 2 − 2 cos

2 + 2 − 2 cos

2 | |

||

2 sec

− 2 tan

, 2 =

+

=

+

,

1

1

2

1

2

N

=

17. (a) Distance = rate × time, so time = distancerate. 1 =

3 =

(b)

2

√

2 + 2 /4

42 + 2

=

.

1

1

2

2

2

=

· sec tan − sec2 = 0 when 2 sec

1

2

1 sin

1 1

−

=0 ⇒

1 cos

2 cos

sin

1

=

1 cos

2 cos

1

1

tan − sec

1

2

⇒ sin =

=0 ⇒

1

. The First Derivative Test shows that this gives

2

a minimum.

(c) Using part (a) with = 1 and 1 = 026, we have 1 =

2

42 + 2 = 3 2

1

⇒ =

1

2

1

⇒ 1 =

1

026

≈ 385 kms. 3 =

√

42 + 2

1

⇒

1

2 2 − 2 = 1 (034)2 (1026)2 − 12 ≈ 042 km. To ﬁnd 2 , we use sin =

3 1

2

2

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

186

¤

CHAPTER 3 PROBLEMS PLUS

from part (b) and 2 =

2 sec

− 2 tan

+

from part (a). From the ﬁgure,

1

2

1

2

2

1

⇒ sec = 2 and tan = 2

, so

2 − 2

2 − 2

1

1

2 − 2 − 21

22

2

1

2 = 2

+

. Using the values for 2 [given as 0.32],

1 2 − 2

2 2 − 2

1

2

1

sin =

2 − 2 − 21

22

2

1

, 1 , and we can graph Y1 = 2 and Y2 = 2

+

and ﬁnd their intersection points.

1 2 − 2

2 2 − 2

1

2

1

Doing so gives us 2 ≈ 410 and 766, but if 2 = 410, then = arcsin(1 2 ) ≈ 696◦ , which implies that point is to the left of point in the diagram. So 2 = 766 kms.

Let = | | and = | | as shown in the ﬁgure.

19.

e

Since = | | + | |, | | = − . Now

Let () =

1

2

−12

2

−12

−

.

(−2) − 1 2 + 2 − 2

(−2) = √

+√

− 2

2

2 − 2

2 + 2 − 2

0 () = 0 ⇒

Fo

0 () =

√

√

2 − 2 + − 2 + 2 − 2.

rS

al

|| = | | + | | = + −

√

2 − 2 + − ( − )2 + 2

√

2

√

= 2 − 2 + − ( − )2 +

2 − 2

√

√

= 2 − 2 + − 2 − 2 + 2 + 2 − 2

√

= √

2 − 2

2 + 2 − 2

⇒

2

2

= 2

2 − 2

+ 2 − 2

⇒

ot

2 2 + 2 2 − 23 = 2 2 − 2 2 ⇒ 0 = 23 − 22 2 − 2 2 + 2 2 ⇒

⇒ 0 = 22 ( − ) − 2 ( + )( − ) ⇒ 0 = ( − ) 22 − 2 ( + )

0 = 22 ( − ) − 2 2 − 2

N

But , so 6= . Thus, we solve 22 − 2 − 2 = 0 for :

√

− −2 ± (−2 )2 − 4(2)(−2 )

√

2 ± 4 + 8 2 2

=

. Because 4 + 82 2 2 , the “negative” can be

=

2(2)

4

√ √

√

√

2 + 2 + 82

2 + 2 2 + 82

=

[ 0] =

+ 2 + 82 . The maximum discarded. Thus, =

4

4

4

value of || occurs at this value of .

21. =

4

3

3

⇒

Therefore, 42

= 42

. But is proportional to the surface area, so

= · 42 for some constant .

= · 42

⇔

= = constant. An antiderivative of with respect to is , so = + .

When = 0, the radius must equal the original radius 0 , so = 0 , and = + 0 . To ﬁnd we use the fact that

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

CHAPTER 3 PROBLEMS PLUS

3

3 when = 3, = 3 + 0 and = 1 0 ⇒ 4 (3 + 0 )3 = 1 · 4 0 ⇒ (3 + 0 )3 = 1 0 ⇒

2

3

2

3

2

1

1

1

3 + 0 = √ 0 ⇒ = 1 0 √ − 1 . Since = + 0 , = 1 0 √ − 1 + 0 . When the snowball

3

3

3

3

3

2

2

has melted completely we have = 0 ⇒

2

1

3 0

1

√

3

2

√

332

− 1 + 0 = 0 which gives = √

. Hence, it takes

3

2−1

N

ot

Fo

rS

al

e

√

332

3

√

−3= √

≈ 11 h 33 min longer.

3

3

2−1

2−1

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

¤

187

N ot e

al

rS

Fo

4

INTEGRALS

4.1 Areas and Distances

1. (a) Since is increasing, we can obtain a lower estimate by using left

endpoints. We are instructed to use four rectangles, so = 4.

4

8−0

−

=

=2

4 =

(−1 ) ∆

∆ =

4

=1

= (0 ) · 2 + (1 ) · 2 + (2 ) · 2 + (3 ) · 2

= 2[ (0) + (2) + (4) + (6)]

Since is increasing, we can obtain an upper estimate by using right

al

endpoints.

4

4 =

( ) ∆

e

= 2(2 + 375 + 5 + 575) = 2(165) = 33

rS

=1

= (1 ) · 2 + (2 ) · 2 + (3 ) · 2 + (4 ) · 2

= 2[ (2) + (4) + (6) + (8)]

= 2(375 + 5 + 575 + 6) = 2(205) = 41

Fo

Comparing 4 to 4 , we see that we have added the area of the rightmost upper rectangle, (8) · 2, to the sum and

subtracted the area of the leftmost lower rectangle, (0) · 2, from the sum.

8

8−0

=1

(−1 )∆

∆ =

(b) 8 =

8

=1

ot

= 1[ (0 ) + (1 ) + · · · + (7 )]

= (0) + (1) + · · · + (7)

N

≈ 2 + 30 + 375 + 44 + 5 + 54 + 575 + 59

= 352

8 =

8

( )∆ = (1) + (2) + · · · + (8)

add rightmost upper rectangle,

= 8 + 1 · (8) − 1 · (0)

=1

subtract leftmost lower rectangle

= 352 + 6 − 2 = 392

3. (a) 4 =

4

=1

( ) ∆

∆ =

2 − 0

=

4

8

= [ (1 ) + (2 ) + (3 ) + (4 )] ∆

= cos + cos 2 + cos 3 + cos 4

8

8

8

8 8

=

4

=1

( ) ∆

≈ (09239 + 07071 + 03827 + 0) ≈ 07908

8

Since is decreasing on [0 2], an underestimate is obtained by using the right endpoint approximation, 4 . c ° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

189

190

¤

CHAPTER 4

(b) 4 =

4

INTEGRALS

(−1 ) ∆ =

=1

4

=1

(−1 ) ∆

= [(0 ) + (1 ) + (2 ) + (3 )] ∆

= cos 0 + cos + cos 2 + cos 3

8

8

8 8

≈ (1 + 09239 + 07071 + 03827) ≈ 11835

8

4 is an overestimate. Alternatively, we could just add the area of the leftmost upper rectangle and subtract the area of the

rightmost lower rectangle; that is, 4 = 4 + (0) · − · .

8

2

8

2 − (−1)

=1 ⇒

3

3 = 1 · (0) + 1 · (1) + 1 · (2) = 1 · 1 + 1 · 2 + 1 · 5 = 8.

5. (a) () = 1 + 2 and ∆ =

2 − (−1)

= 05 ⇒

6

6 = 05[ (−05) + (0) + (05) + (1) + (15) + (2)]

∆ =

e

= 05(125 + 1 + 125 + 2 + 325 + 5)

rS

(b) 3 = 1 · (−1) + 1 · (0) + 1 · (1) = 1 · 2 + 1 · 1 + 1 · 2 = 5

al

= 05(1375) = 6875

6 = 05[ (−1) + (−05) + (0) + (05) + (1) + (15)]

= 05(2 + 125 + 1 + 125 + 2 + 325)

Fo

= 05(1075) = 5375

(c) 3 = 1 · (−05) + 1 · (05) + 1 · (15)

ot

= 1 · 125 + 1 · 125 + 1 · 325 = 575

6 = 05[(−075) + (−025) + (025)

N

+ (075) + (125) + (175)]

= 05(15625 + 10625 + 10625 + 15625 + 25625 + 40625)

= 05(11875) = 59375

(d) 6 appears to be the best estimate.

7. () = 2 + sin , 0 ≤ ≤ , ∆ = .

= 2:

The maximum values of on both subintervals occur at =

upper sum = · + ·

2

2

2

2

=3·

2

+3·

2

,

2

so

= 3 ≈ 942.

The minimum values of on the subintervals occur at = 0 and

= , so lower sum = (0) ·

=2·

2

2

+ () ·

+2·

2

2

= 2 ≈ 628.

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

SECTION 4.1

= 4:

= 8:

AREAS AND DISTANCES

¤

191

upper sum = + + + 3

4

2

2

4

4

√

√

= 2 + 1 2 + (2 + 1) + (2 + 1) + 2 + 1 2

2

2

4

√

= 10 + 2 ≈ 896

4

lower sum = (0) + 4 + 3 + ()

4

4

√

√

1

1

= (2 + 0) + 2 + 2 2 + 2 + 2 2 + (2 + 0)

4

√

= 8 + 2 4 ≈ 739

upper sum = + + 3 + +

8

4

8

2

2

5

3

7

+ 8 + 4 + 8

8

≈ 865

lower sum = (0) + + + 3 + 5

8

4

8

8

+ 3 + 7 + ()

4

8

8

e

≈ 786

al

9. Here is one possible algorithm (ordered sequence of operations) for calculating the sums:

1 Let SUM = 0, X_MIN = 0, X_MAX = 1, N = 10 (depending on which sum we are calculating),

rS

DELTA_X = (X_MAX - X_MIN)/N, and RIGHT_ENDPOINT = X_MIN + DELTA_X.

2 Repeat steps 2a, 2b in sequence until RIGHT_ENDPOINT X_MAX.

2a Add (RIGHT_ENDPOINT)^4 to SUM.

Fo

Add DELTA_X to RIGHT_ENDPOINT.

At the end of this procedure, (DELTA_X)·(SUM) is equal to the answer we are looking for. We ﬁnd that

100 =

1 100

100 =1

4

≈ 02533, 30

100

4

10

30

1

=

30 =1

30

4

≈ 02170, 50

50

1

=

50 =1

50

4

≈ 02101 and

ot

10

10

1

=

10 =1

≈ 02050. It appears that the exact area is 02. The following display shows the program

N

SUMRIGHT and its output from a TI-83/4 Plus calculator. To generalize the program, we have input (rather than assign) values for Xmin, Xmax, and N. Also, the function, 4 , is assigned to Y1 , enabling us to evaluate any right sum

merely by changing Y1 and running the program.

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

192

¤

CHAPTER 4

INTEGRALS

11. In Maple, we have to perform a number of steps before getting a numerical answer. After loading the student package

[command: with(student);] we use the command left_sum:=leftsum(1/(xˆ2+1),x=0..1,10 [or 30, or 50]); which gives us the expression in summation notation. To get a numerical approximation to the sum, we use evalf(left_sum);. Mathematica does not have a special command for these sums, so we must type them in manually. For example, the ﬁrst left sum is given by

(1/10)*Sum[1/(((i-1)/10)ˆ2+1)],{i,1,10}], and we use the N command on the resulting output to get a numerical approximation.

In Derive, we use the LEFT_RIEMANN command to get the left sums, but must deﬁne the right sums ourselves.

(We can deﬁne a new function using LEFT_RIEMANN with ranging from 1 to instead of from 0 to − 1.)

2

1

1

1

, 0 ≤ ≤ 1, the left sums are of the form =

. Speciﬁcally, 10 ≈ 08100,

+1

=1 −1 2 + 1

1

1

. Speciﬁcally, 10 ≈ 07600,

=1 2 + 1

al

30 ≈ 07937, and 50 ≈ 07904. The right sums are of the form =

e

(a) With () =

30 ≈ 07770, and 50 ≈ 07804.

rS

(b) In Maple, we use the leftbox (with the same arguments as left_sum) and rightbox commands to generate the

Fo

graphs.

left endpoints, = 30

left endpoints, = 50

N

ot

left endpoints, = 10

right endpoints, = 10

right endpoints, = 30

right endpoints, = 50

(c) We know that since = 1(2 + 1) is a decreasing function on (0 1), all of the left sums are larger than the actual area, and all of the right sums are smaller than the actual area. Since the left sum with = 50 is about 07904 0791 and the right sum with = 50 is about 07804 0780, we conclude that 0780 50 exact area 50 0791, so the exact area is between 0780 and 0791.

13. Since is an increasing function, 6 will give us a lower estimate and 6 will give us an upper estimate.

6 = (0 fts)(05 s) + (62)(05) + (108)(05) + (149)(05) + (181)(05) + (194)(05) = 05(694) = 347 ft

6 = 05(62 + 108 + 149 + 181 + 194 + 202) = 05(896) = 448 ft c ° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

SECTION 4.1

AREAS AND DISTANCES

¤

193

15. Lower estimate for oil leakage: 5 = (76 + 68 + 62 + 57 + 53)(2) = (316)(2) = 632 L.

Upper estimate for oil leakage: 5 = (87 + 76 + 68 + 62 + 57)(2) = (35)(2) = 70 L.

17. For a decreasing function, using left endpoints gives us an overestimate and using right endpoints results in an underestimate.

We will use 6 to get an estimate. ∆ = 1, so

6 = 1[(05) + (15) + (25) + (35) + (45) + (55)] ≈ 55 + 40 + 28 + 18 + 10 + 4 = 155 ft

For a very rough check on the above calculation, we can draw a line from (0 70) to (6 0) and calculate the area of the triangle: 1 (70)(6) = 210. This is clearly an overestimate, so our midpoint estimate of 155 is reasonable.

2

2

, 1 ≤ ≤ 3. ∆ = (3 − 1) = 2 and = 1 + ∆ = 1 + 2.

2 + 1

→∞

→∞ =1

( )∆ = lim

→∞ =1

2(1 + 2)

2

· .

(1 + 2)2 + 1

√ sin , 0 ≤ ≤ . ∆ = ( − 0) = and = 0 + ∆ = .

= lim = lim

→∞

→∞ =1

al

21. () =

e

= lim = lim

sin() · .

→∞ =1

( ) ∆ = lim

rS

19. () =

tan can be interpreted as the area of the region lying under the graph of = tan on the interval 0 ,

4

→∞ =1 4

4

23. lim

ot

Fo

4 − 0

=

, = 0 + ∆ =

, and ∗ = , the expression for the area is since for = tan on 0 with ∆ =

4

4

4

= lim

. Note that this answer is not unique, since the expression for the area is

(∗ ) ∆ = lim tan

→∞ =1

→∞ =1

4 4

the same for the function = tan( − ) on the interval + , where is any integer.

4

25. (a) Since is an increasing function, is an underestimate of [lower sum] and is an overestimate of [upper sum].

(b)

N

Thus, , , and are related by the inequality .

= (1 )∆ + (2 )∆ + · · · + ( )∆

= (0 )∆ + (1 )∆ + · · · + (−1 )∆

− = ( )∆ − (0 )∆

= ∆[ ( ) − (0 )]

=

−

[ () − ()]

In the diagram, − is the sum of the areas of the shaded rectangles. By sliding the shaded rectangles to the left so that they stack on top of the leftmost shaded rectangle, we form a rectangle of height () − () and width

(c) , so − − ; that is, −

−

.

−

[ () − ()].

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

194

¤

CHAPTER 4 INTEGRALS

2

2−0

2

=

and = 0 + ∆ = .

5

2

325 2

64 5

2

= lim = lim

( ) ∆ = lim

· = lim

· = lim

.

→∞

→∞ =1

→∞ =1

→∞ =1 5 →∞ 6 =1

27. (a) = () = 5 . ∆ =

(b)

CAS

5 =

=1

2 ( + 1)2 22 + 2 − 1

12

2

2

2

2

+ 2 + 1 22 + 2 − 1

64 ( + 1) 2 + 2 − 1

64

= lim (c) lim 6 ·

→∞

12

12 →∞

2 · 2

16

2

2

1

1

=

2+ − 2 = lim 1 + + 2

3 →∞

29. = () = cos . ∆ =

16

3

·1·2=

32

3

−0

= and = 0 + ∆ = .

then = sin = 1.

2

rS

2,

If =

al

e

1

+1

sin

2

CAS

CAS

= sin

·

( ) ∆ = lim cos = lim

= lim = lim

−

→∞

→∞ =1

→∞ =1

→∞

2

2 sin

2

4.2 The Definite Integral

14 − 2

−

=

= 2.

6

Fo

1. () = 3 − 1 , 2 ≤ ≤ 14. ∆ =

2

Since we are using left endpoints, ∗ = −1 .

6

6 =

(−1 ) ∆

=1

ot

= (∆) [ (0 ) + (1 ) + (2 ) + (3 ) + (4 ) + (5 )]

= 2[ (2) + (4) + (6) + (8) + (10) + (12)]

N

= 2[2 + 1 + 0 + (−1) + (−2) + (−3)] = 2(−3) = −6

The Riemann sum represents the sum of the areas of the two rectangles above the -axis minus the sum of the areas of the three rectangles below the -axis; that is, the net area of the rectangles with respect to the -axis.

3. 5 =

5

( ) ∆

=1

[∗ = = 1 (−1 + ) is a midpoint and ∆ = 1]

2

= 1 [(15) + (25) + (35)

+ (45) + (55)]

[ () =

√

− 2]

≈ −0856759

The Riemann sum represents the sum of the areas of the two rectangles above the -axis minus the sum of the areas of the three rectangles below the -axis.

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

SECTION 4.2 THE DEFINITE INTEGRAL

5. (a)

(b)

() ≈ 5 = [ (2) + (4) + (6) + (8) + (10)] ∆

= [−1 + 0 + (−2) + 2 + 4](2) = 3(2) = 6

10

() ≈ 5 = [ (0) + (2) + (4) + (6) + (8)] ∆

0

(c)

0

195

10

0

¤

= [3 + (−1) + 0 + (−2) + 2](2) = 2(2) = 4

10

() ≈ 5 = [ (1) + (3) + (5) + (7) + (9)] ∆

= [0 + (−1) + (−1) + 0 + 3](2) = 1(2) = 2

7. Since is increasing, 5 ≤

Lower estimate = 5 =

30

5

10

() ≤ 5 .

(−1 )∆ = 4[ (10) + (14) + (18) + (22) + (26)]

=1

5

()∆ = 4[ (14) + (18) + (22) + (26) + (30)]

al

Upper estimate = 5 =

e

= 4[−12 + (−6) + (−2) + 1 + 3] = 4(−16) = −64

=1

rS

= 4[−6 + (−2) + 1 + 3 + 8] = 4(4) = 16

9. ∆ = (8 − 0)4 = 2, so the endpoints are 0, 2, 4, 6, and 8, and the midpoints are 1, 3, 5, and 7. The Midpoint Rule gives

0

sin

4

√

√

√

√

√

≈

(¯ ) ∆ = 2 sin 1 + sin 3 + sin 5 + sin 7 ≈ 2(30910) = 61820.

=1

11. ∆ = (2 − 0)5 =

gives

0

2

so the endpoints are 0, 2 , 4 , 6 , 8 , and 2, and the midpoints are 1 , 3 , 5 ,

5 5 5 5

5 5 5

5

2

≈

(¯ ) ∆ =

+1

5

=1

1

5

1

5

+1

+

ot

2

,

5

Fo

8

3

5

3

5

+1

+

5

5

5

5

+1

+

7

5

7

5

+1

+

9

5

9

5

+1

=

2

5

7

5

127

56

and 9 . The Midpoint Rule

5

=

127

≈ 09071.

140

N

13. In Maple 14, use the commands with(Student[Calculus1]) and

ReimannSum(x/(x+1),0..2,partition=5,method=midpoint,output=plot). In some older versions of

Maple, use with(student) to load the sum and box commands, then m:=middlesum(x/(x+1),x=0..2), which gives us the sum in summation notation, then M:=evalf(m) to get the numerical approximation, and ﬁnally middlebox(x/(x+1),x=0..2) to generate the graph. The values obtained for = 5, 10, and 20 are 09071, 09029, and

09018, respectively.

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

¤

196

CHAPTER 4 INTEGRALS

15. We’ll create the table of values to approximate

0

sin by using the

program in the solution to Exercise 4.1.9 with Y1 = sin , Xmin = 0,

5

17. On [2 6], lim

1 − 2

∆ =

4 + 2

→∞ =1

19. On [2 7], lim

2

6

1983524

50

1999342

100

The values of appear to be approaching 2.

1933766

10

Xmax = , and = 5, 10, 50, and 100.

1999836

1 − 2

.

4 + 2

[5(∗ )3 − 4∗ ] ∆ =

→∞ =1

7

2

(53 − 4) .

3

5−2

3

= and = 2 + ∆ = 2 + .

5

3

3 3

3

= lim

(4 − 2) = lim

( ) ∆ = lim

2+

4−2 2+

→∞ =1

→∞ =1

→∞ =1

2

3

3

6

18

( + 1)

6

−

= lim

= lim

−

= lim − 2

→∞ =1

→∞

→∞

=1

2

18

1

+1

= lim −

= −9 lim 1 +

= −9(1) = −9

→∞

→∞

2

23. Note that ∆ =

rS

al

e

21. Note that ∆ =

2

0 − (−2)

2

= and = −2 + ∆ = −2 + .

2

2

2

2 2

2

−2 +

= lim

( + ) = lim

( ) ∆ = lim

−2 +

+ −2 +

→∞ =1

→∞ =1

→∞ =1

−2

0

2

Fo

2

2 42

42

2

6

8

+ 2 −2+

= lim

+2

−

4−

→∞ =1

→∞ =1

2

8 ( + 1)(2 + 1)

2 4 2 6

12 ( + 1)

2

= lim

− 2

+ · (2)

−

+

2 = lim

→∞ 2 =1

→∞ 3

=1

6

2

=1

4 ( + 1)(2 + 1)

4 + 1 2 + 1

1

+1

= lim

+ 4 = lim

−6 1+

+4

−6

→∞ 3

→∞ 3

2

4

1

1

1

4

2

= lim

1+

2+

−6 1+

+ 4 = (1)(2) − 6(1) + 4 =

→∞ 3

3

3

N

ot

= lim

25. Note that ∆ =

0

1

1−0

1

= and = 0 + ∆ = .

2

3

1

∆ = lim

( − 3 ) = lim

( ) ∆ = lim

−3

→∞ =1

→∞ =1

→∞ =1

3

2

1 3

1 1 3

32

3 2

− 2 = lim

− 2

→∞ =1 3

→∞ 3 =1

=1

2

1 ( + 1)

1 +1 +1

1 + 1 2 + 1

3 ( + 1)(2 + 1)

= lim

−

− 3

= lim

→∞

→∞ 4

4

2

6

2

1

1

1

1

1

1

1

1

3

1+

1+

−

1+

2+

= (1)(1) − (1)(2) = −

= lim

→∞ 4

2

4

2

4

= lim

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

SECTION 4.2 THE DEFINITE INTEGRAL

¤

197

( − )

−

( − )2

−

= lim

27.

= lim

1+

+

→∞

→∞

=1

2

=1

=1

( − )

( − )2

( − )2 ( + 1)

1

+

= ( − ) + lim

1+

·

→∞

→∞

2

2

2

2

= ( − ) + 1 ( − )2 = ( − ) + 1 − 1 = ( − ) 1 ( + ) = 1 − 2

2

2

2

2

2

= lim

29. () =

so

6

2

6−2

4

4

, = 2, = 6, and ∆ =

= . Using Theorem 4, we get ∗ = = 2 + ∆ = 2 + ,

1 + 5

= lim = lim

→∞

→∞ =1

1 + 5

4

2+

4

5 · .

4

1+ 2+

31. ∆ = ( − 0) = and ∗ = = .

33. (a) Think of

so

5

0

2

0

2

0

() = 1 (1 + 3)2 = 4.

2

() =

5

9

7

() +

1

(1

2

3

2

() +

rectangle

+ 3)2 +

3·1

5

3

triangle

+

1

2

·2·3

= 4 + 3 + 3 = 10

7

5

() = − 1 · 2 · 3 = −3.

2

() is the negative of the area of a trapezoid with bases 3 and 2 and height 2, so it equals

+ ) = − 1 (3 + 2)2 = −5. Thus,

2

5

7

9

9

() = 0 () + 5 () + 7 () = 10 + (−3) + (−5) = 2.

0

−1

(1 − ) can be interpreted as the difference of the areas of the two

shaded triangles; that is, 1 (2)(2) − 1 (1)(1) = 2 −

2

2

37.

()

() is the negative of the area of the triangle with base 2 and height 3.

N

2

0

trapezoid

− 1 (

2

35.

2

ot

(d)

7

e

() as the area of a trapezoid with bases 1 and 3 and height 2. The area of a trapezoid is = 1 ( + ),

2

=

(c)

al

0

(b)

2

1

5 CAS

5 CAS

2

(sin 5 )

= lim

= sin = lim cot =

→∞ =1

→∞ =1

→∞

2

5

5

sin 5 = lim

rS

Fo

1

2

= 3.

2

√

0

1 + 9 − 2 can be interpreted as the area under the graph of

−3

√

() = 1 + 9 − 2 between = −3 and = 0. This is equal to one-quarter the area of the circle with radius 3, plus the area of the rectangle, so

√

0

1 + 9 − 2 = 1 · 32 + 1 · 3 = 3 + 9 .

4

4

−3

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

¤

198

39.

CHAPTER 4 INTEGRALS

2

−1

|| can be interpreted as the sum of the areas of the two shaded

triangles; that is, 1 (1)(1) + 1 (2)(2) =

2

2

1

2

= 5.

2

4

2

+

0

47.

49.

51.

1

0

4

1

sin2 cos4 = 0 since the limits of intergration are equal.

(5 − 62 ) =

3

0

5 − 6

4

1

0

2 = 5(1 − 0) − 6 1 = 5 − 2 = 3

3

2 − 3

1

() +

5

2

() −

[2 () + 3()] = 2

3

3

4

+

1

−1

−2

9

2

4

1

1

= 2 · 1 (4 − 1 ) − 3 · 1 (4 − 12 ) + 1(4 − 1) =

3

2

−2

0

0

(22 − 3 + 1) = 2

2

9

1

() =

=

0

−2

5

9

() + 3

0

5

−1

() +

()

−2

−1

45

2

()

= 225

[by Property 5 and reversing limits]

[Property 5]

e

45.

al

43.

() = 2(37) + 3(16) = 122

() is clearly less than −1 and has the smallest value. The slope of the tangent line of at = 1, 0 (1), has a value

rS

41.

between −1 and 0, so it has the next smallest value. The largest value is

value about 1 unit less than

8

3

2

−4

() 0 (1)

[ () + 2 + 5] =

2

−4

8

0

()

() + 2

2

−4

8

1 = −3 [area below -axis]

4

()

+

ot

53. =

Fo

0

3

() , followed by

() . Still positive, but with a smaller value than

quantities from smallest to largest gives us

3

8

2

−4

8

3

8

4

8

4

() , is

() , which has a

8

0

() . Ordering these

() or B E A D C

5 = 1 + 22 + 3

+ 3 − 3 = −3

N

2 = − 1 (4)(4) [area of triangle, see ﬁgure]

2

+ 1 (2)(2)

2

= −8 + 2 = −6

3 = 5[2 − (−4)] = 5(6) = 30

Thus, = −3 + 2(−6) + 30 = 15.

55. 2 − 4 + 4 = ( − 2)2 ≥ 0 on [0 4], so

4

0

(2 − 4 + 4) ≥ 0 [Property 6].

√

√

1 + 2 ≤ 2 and

√

√

1 √

1 √

1[1 − (−1)] ≤ −1 1 + 2 ≤ 2 [1 − (−1)] [Property 8]; that is, 2 ≤ −1 1 + 2 ≤ 2 2.

57. If −1 ≤ ≤ 1, then 0 ≤ 2 ≤ 1 and 1 ≤ 1 + 2 ≤ 2, so 1 ≤

59. If 1 ≤ ≤ 4, then 1 ≤

61. If

4

≤≤

,

3

4√

4√

√

≤ 2 so 1(4 − 1) ≤ 1 ≤ 2(4 − 1); that is, 3 ≤ 1 ≤ 6.

then 1 ≤ tan ≤

√

√

3

3, so 1 − ≤ 4 tan ≤ 3 − or

3

4

3

4

12

≤

3

4

tan ≤

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

12

√

3.

SECTION 4.3 THE FUNDAMENTAL THEOREM OF CALCULUS

63. For −1 ≤ ≤ 1, 0 ≤ 4 ≤ 1 and 1 ≤

or 2 ≤

65.

√

1 √

1 + 4 ≤ 2 2.

−1

¤

199

√

√

√

1 √

1 + 4 ≤ 2, so 1[1 − (−1)] ≤ −1 1 + 4 ≤ 2 [1 − (−1)]

√

√

3√

3

4 + 1 ≥ 4 = 2 , so 1 4 + 1 ≥ 1 2 = 1 33 − 13 =

3

26

.

3

67. Using right endpoints as in the proof of Property 2, we calculate

() = lim

→∞ =1

( ) ∆ = lim

→∞

( ) ∆ = lim

→∞ =1

=1

69. Suppose that is integrable on [0 1] that is, lim

→∞ =1

( ) ∆ =

() .

(∗ ) ∆ exists for any choice of ∗ in [−1 ]. Let n denote a

1

1 2

−1

positive integer and divide the interval [0 1] into n equal subintervals 0

,

, ,

1 . If we choose ∗ to be

a rational number in the ith subinterval, then we obtain the Riemann sum

→∞ =1

=1

(∗ ) ·

(∗ ) ·

lim

→∞ =1

1

= lim 0 = 0. Now suppose we choose ∗ to be an irrational number. Then we get

→∞

al

1

= 0, so

1

1

1

1

1 · = · = 1 for each , so lim

(∗ ) · = lim 1 = 1. Since the value of

=

→∞ =1

→∞

=1

rS

lim

(∗ ) ·

e

=1

(∗ ) ∆ depends on the choice of the sample points ∗ , the limit does not exist, and is not integrable on [0 1].

4

4 1

4 1

. At this point, we need to recognize the limit as being of the form

= lim

· = lim

→∞ =1 5

→∞ =1 4

→∞ =1

→∞ =1

is

1

0

( ) ∆, where ∆ = (1 − 0) = 1, = 0 + ∆ = , and () = 4 . Thus, the deﬁnite integral

4 .

√

73. Choose = 1 + and ∗ = −1 =

1

1

1

= lim

−1

→∞ =1 1 +

→∞ =1 ( + − 1)( + )

1+

−1

1

1

1

1

−

[by the hint] = lim

−

= lim

→∞ =1

→∞

+−1

+

=0 +

=1 +

1

1

1

1

1

1

+

+··· +

−

+ ··· +

+

= lim

→∞

+1

2 − 1

+1

2 − 1

2

1

1

= lim

−

= lim 1 − 1 = 1

2

2

→∞

→∞

2

N

2

−1

1+

1+

. Then

ot

lim

Fo

71. lim

1

−2 = lim

4.3 The Fundamental Theorem of Calculus

1. One process undoes what the other one does. The precise version of this statement is given by the Fundamental Theorem of

Calculus. See the statement of this theorem and the paragraph that follows it on page 317. c ° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

200

¤

CHAPTER 4 INTEGRALS

3. (a) () =

() .

0

0

(0) =

0

1

(1) =

0

2

(2) =

0

() = 0

() = 1 · 2 = 2

[rectangle],

1

2

2

() = 0 () + 1 () = (1) + 1 ()

=2+1·2+ 1 ·1·2 =5

[rectangle plus triangle],

2

3

3

(3) = 0 () = (2) + 2 () = 5 + 1 · 1 · 4 = 7,

2

6

(6) = (3) + 3 ()

[the integral is negative since lies under the -axis]

1

=7+ − 2 ·2·2+1·2 =7−4 =3

(b) is increasing on (0 3) because as increases from 0 to 3, we keep

(d)

adding more area.

e

(c) has a maximum value when we start subtracting area; that is,

al

at = 3.

(a) By FTC1 with () = 2 and = 1, () =

rS

5.

0 () = () = 2 .

7. () =

1 and () =

3 + 1

1

1

1

2 ⇒

1 3

1 3

3 1 = 3 −

2 =

1

3

⇒ 0 () = 2 .

Fo

(b) Using FTC2, () =

1

1

, so by FTC1, 0 () = () = 3

. Note that the lower limit, 1, could be any

3 + 1

+1

ot

real number greater than −1 and not affect this answer.

11. () =

13. Let =

0 () =

5

( − 2 )8 , so by FTC1, 0 () = () = ( − 2 )8 .

N

9. () = ( − 2 )8 and () =

√

1 + sec = −

√

1 + sec ⇒ 0 () = −

√

√

1 + sec = − 1 + sec

1

1

. Then

= − 2 . Also,

=

, so

1

sin4 =

2

2

sin4 ·

− sin4 (1)

= sin4

=

.

2

= sec2 . Also,

=

, so

tan

√

√

√

√

= +

= tan + tan sec2 .

+ =

+ ·

0 =

0

0

15. Let = tan . Then

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

¤

SECTION 4.3 THE FUNDAMENTAL THEOREM OF CALCULUS

= −3. Also,

=

, so

1

3(1 − 3)3

3

3

3

3

=

·

·

(−3) =

=−

=−

1 + 2

1 + 2

1 1 + 2

1 + 2

1 + (1 − 3)2

17. Let = 1 − 3. Then

0 =

1−3

4

4

2

3

2

(−1)4

− 2 =

− 2

− 22 −

− (−1)2 = (4 − 4) − 1 − 1 = 0 − − 3 =

=

4

4

4

4

4

−1

−1

2

1

4

(5 − 2 + 32 ) = 5 − 2 + 3 1 = (20 − 16 + 64) − (5 − 1 + 1) = 68 − 5 = 63

9

√

=

1

6

27.

( + 2)( − 3) =

9

1

31.

33.

35.

0

2

1

=

1

2

3

9

32 = 2 (932 − 132 ) = 2 (27 − 1) =

3

3

1

(2 − − 6) =

9

1

3

3

1

− 1 2 − 6 0 = 1 −

2

3

4

sec2 = tan 0 = tan − tan 0 = 1 − 0 = 1

4

5 + 3 6

=

4

2

1

2

2

(1 + 4 + 42 ) = + 2 2 + 4 3 1 = 2 + 8 +

3

1

37. If () =

sin

0

cos

() =

32

3

2

+ 3 2 = 1 2 + 3 1 = (2 + 8) − 1 + 1 =

2

2

if 0 ≤ 2

N

1

(1 + 2)2 =

2

0

1

9

52

3

1

2

− 6 − 0 = − 37

6

9

9

1

√ −√

(12 − −12 ) = 2 32 − 212

=

3

1

1

1

2

2

4 40

= 3 · 27 − 2 · 3 − 3 − 2 = 12 − − 3 = 3

−1

√ =

4

6

32

32

√

√

= − cos − − cos = −(−1) − − 32 = 1 + 32

6

sin = − cos

1

0

29.

12 =

1

9

ot

25.

e

4

3

4

al

23.

1

rS

21.

Fo

19.

if 2 ≤ ≤

2

0

sin +

− 1+2+ 4 =

3

62

3

−

13

3

=

49

3

17

2

then

2

= −0 + 1 + 0 − 1 = 0

2

cos = − cos 0 + sin 2 = − cos + cos 0 + sin − sin

2

2

Note that is integrable by Theorem 3 in Section 4.2.

39. () = −4 is not continuous on the interval [−2 1], so FTC2 cannot be applied. In fact, has an inﬁnite discontinuity at

= 0, so

1

−2

201

−4 does not exist.

41. () = sec tan is not continuous on the interval [3 ], so FTC2 cannot be applied. In fact, has an inﬁnite

discontinuity at = 2, so

3

sec tan does not exist.

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

202

¤

CHAPTER 4 INTEGRALS

43. From the graph, it appears that the area is about 60. The actual area is

27

0

13 =

3 43

4

27

3

4

=

0

· 81 − 0 =

= 6075. This is

243

4

3

4

of the

area of the viewing rectangle.

45. It appears that the area under the graph is about

2

3

of the area of the viewing

rectangle, or about 2 ≈ 21. The actual area is

3

sin = [− cos ] = (− cos ) − (− cos 0) = − (−1) + 1 = 2.

0

0

−1

3 =

1

4

4

2

−1

1

4

=

0

2 − 1

+

2 + 1

=4−

15

4

= 375

e

2

49. () =

3

2

2 − 1

=

2 + 1

2

2

51. () =

3

0

2 − 1

= −

2 + 1

2

2

0

2 − 1

+

2 + 1

2

3

0

2 − 1

⇒

2 + 1

2

(3) − 1

4 − 1

9 − 1

(2) − 1

·

(2) +

·

(3) = −2 · 2

+3· 2

(2)2 + 1

(3)2 + 1

4 + 1

9 + 1

3

√

cos(2 ) =

0

√

Fo

0 () = −

rS

al

47.

cos(2 ) +

0

3

cos(2 ) = −

√

cos(2 ) +

0

3

0

cos(2 ) ⇒

0

00 =

2

2

⇒ 0 = 2

2 + + 2

++2

N

53. =

ot

√

√

1

2

0 () = − cos ( ) ·

( ) + [cos(3 )2 ] ·

(3 ) = − √ cos + 32 cos(6 )

2

⇒

(2 + + 2)(2) − 2 (2 + 1)

23 + 22 + 4 − 23 − 2

2 + 4

( + 4)

=

= 2

= 2

.

2 + + 2)2

2 + + 2)2

(

(

( + + 2)2

( + + 2)2

The curve is concave downward when 00 0; that is, on the interval (−4 0).

55. By FTC2,

4

1

0 () = (4) − (1), so 17 = (4) − 12 ⇒ (4) = 17 + 12 = 29.

57. (a) The Fresnel function () =

0

sin 2 has local maximum values where 0 = 0 () = sin 2 and

2

2

0 changes from positive to negative. For 0, this happens when 2 = (2 − 1) [odd multiples of ] ⇔

2

√

2 = 2(2 − 1) ⇔ = 4 − 2, any positive integer. For 0, 0 changes from positive to negative where

√

2

= 2 [even multiples of ] ⇔ 2 = 4 ⇔ = −2 . 0 does not change sign at = 0.

2

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

SECTION 4.3 THE FUNDAMENTAL THEOREM OF CALCULUS

¤

203

(b) is concave upward on those intervals where 00 () 0. Differentiating our expression for 0 (), we get

00 () = cos 2 2 = cos 2 . For 0, 00 () 0 where cos( 2 ) 0 ⇔ 0 2 or

2

2

2

2

2

2

√

√

2 − 1 2 2 + 1 , any integer ⇔ 0 1 or 4 − 1 4 + 1, any positive integer.

2

2

2

00

For 0, () 0 where cos( 2 ) 0 ⇔ 2 − 3 2 2 − 1 , any integer ⇔

2

2

2

2

√

√

√

√

4 − 3 2 4 − 1 ⇔

4 − 3 || 4 − 1 ⇒

4 − 3 − 4 − 1 ⇒

√

√

√

√

− 4 − 3 − 4 − 1, so the intervals of upward concavity for 0 are − 4 − 1 − 4 − 3 , any

√

√

√ √ √ positive integer. To summarize: is concave upward on the intervals (0 1), − 3 −1 ,

3 5 , − 7 − 5 ,

√

7 3 , .

(c) In Maple, we use plot({int(sin(Pi*tˆ2/2),t=0..x),0.2},x=0..2);. Note that

Maple recognizes the Fresnel function, calling it FresnelS(x). In Mathematica, we use

Fo

rS

al

e

Plot[{Integrate[Sin[Pi*tˆ2/2],{t,0,x}],0.2},{x,0,2}]. In Derive, we load the utility ﬁle

FRESNEL and plot FRESNEL_SIN(x). From the graphs, we see that 0 sin 2 = 02 at ≈ 074.

2

59. (a) By FTC1, 0 () = (). So 0 () = () = 0 at = 1 3 5 7, and 9. has local maxima at = 1 and 5 (since = 0

changes from positive to negative there) and local minima at = 3 and 7. There is no local maximum or minimum at

= 9, since is not deﬁned for 9.

5

0

9

3

5

7

9

= (1) − 1 + 3 , and (9) = 0 = (5) − 5 + 7 . Thus,

N

(5) =

ot

3

5

7

9

1

1

(b) We can see from the graph that 0 1 3 5 7 . So (1) = 0 ,

(1) (5) (9), and so the absolute maximum of () occurs at = 9.

(c) is concave downward on those intervals where 00 0. But 0 () = (),

so 00 () = 0 (), which is negative on (approximately) 1 2 , (4 6) and

2

(d)

(8 9). So is concave downward on these intervals.

3

1−0

= lim

→∞ =1 4

→∞

=1

61. lim

3 1

4 1

1

=

3 =

=

4 0

4

0

63. Suppose 0. Since is continuous on [ + ], the Extreme Value Theorem says that there are numbers and in

[ + ] such that () = and () = , where and are the absolute minimum and maximum values of on

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

¤

204

CHAPTER 4 INTEGRALS

[ + ]. By Property 8 of integrals, (−) ≤

+

() ≤ (−); that is, ()(−) ≤ −

Since − 0, we can divide this inequality by −: () ≤

( + ) − ()

1

=

case where 0.

1

+

() for 6= 0, and hence () ≤

() ≤ ()(−).

() ≤ (). By Equation 2,

+

+

( + ) − ()

≤ (), which is Equation 3 in the

√

√

⇒ 0 () = 1(2 ) 0 for 0 ⇒ is increasing on (0 ∞). If ≥ 0, then 3 ≥ 0, so

√

1 + 3 ≥ 1 and since is increasing, this means that 1 + 3 ≥ (1) ⇒

1 + 3 ≥ 1 for ≥ 0. Next let

65. (a) Let () =

0

1 ≤

1

1 1 √

0 ≤ 0 1 + 3 ≤ + 1 4 0

4

1√

1

1 + 3 ≤ 0 (1 + 3 ) ⇔

0

⇔ 1≤

al

1

1√

1 + 3 ≤ 1 +

0

1

4

= 125.

rS

(b) From part (a) and Property 7:

e

() = 2 − ⇒ 0 () = 2 − 1 ⇒ 0 () 0 when ≥ 1. Thus, is increasing on (1 ∞). And since (1) = 0,

√

√

() ≥ 0 when ≥ 1. Now let = 1 + 3 , where ≥ 0. 1 + 3 ≥ 1 (from above) ⇒ ≥ 1 ⇒ () ≥ 0 ⇒

√

√

1 + 3 − 1 + 3 ≥ 0 for ≥ 0. Therefore, 1 ≤ 1 + 3 ≤ 1 + 3 for ≥ 0.

2

1

2

4 = 2 on [5 10], so

2 +1

+

10

10

10

1

1

2

1

1

1

0≤

= −

=− − −

=

= 01

4 + 2 + 1

2

5

10

5

10

5

5

4

Fo

67. 0

√

()

()

1

= 2 to get 2 = 2 √

⇒ () = 32 .

2

2

√

√

()

To ﬁnd , we substitute = in the original equation to obtain 6 +

= 2 ⇒ 6 + 0 = 2 ⇒

2

√

3 = ⇒ = 9.

() . Then, by FTC1, 0 () = () = rate of depreciation, so () represents the loss in value over the

N

71. (a) Let () =

ot

69. Using FTC1, we differentiate both sides of 6 +

0

interval [0 ].

(b) () =

+ ()

1

() =

+

represents the average expenditure per unit of during the interval [0 ],

0

assuming that there has been only one overhaul during that time period. The company wants to minimize average expenditure.

1

1

1

+

() . Using FTC1, we have 0 () = − 2 +

() + ().

0

0

1

0 () = 0 ⇒ () = +

() ⇒ () =

() = ().

+

0

0

(c) () =

73.

1

9

1

1

=

2

2

1

9

9

1

= 1 ln || = 1 (ln 9 − ln 1) =

2

2

1

1

2

ln 9 − 0 = ln 912 = ln 3

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

SECTION 4.4

75.

√

32

12

6

√

= 6

1 − 2

√

32

12

INDEFINITE INTEGRALS AND THE NET CHANGE THEOREM

¤

√

√32

1

√

= 6 sin−1 12 = 6 sin−1 23 − sin−1 1 = 6 − = 6 =

2

3

6

6

1 − 2

1

77. −1 +1 = +1 −1 = 2 − 0 = 2 − 1 [or start with +1 = 1 ]

1

4.4 Indefinite Integrals and the Net Change Theorem

sin − 1 (sin )3 + = cos − sin3 + =

3

7.

9.

( + 4)(2 + 1) =

11.

3 − 2

4 1 3 1

1 4

1 2

5

−

+

− 2 + = 1 5 − 1 4 + 1 2 − 2 +

− 2 + 4 − 2 =

5

8

8

5

2 4

4 2

√

=

(22 + 9 + 4) = 2

2

2

3

9

+9

+ 4 + = 3 + 2 + 4 +

3

2

3

2

212

3

−

=

(2 − 2−12 ) =

√

3

12

−2

+ = 1 3 − 4 +

3

3

12

( − csc cot ) = 1 2 + csc +

2

(1 + tan2 ) =

sec2 = tan +

cos + 1 = sin + 1 2 + . The members of the family

2

4

N

17.

−1

1

3

1

+

+ = 3 − +

3

−1

3

(2 + −2 ) =

ot

15.

· 3(sin )2 (cos ) + 0

= cos (1 − sin2 ) = cos (cos2 ) = cos3

5.

13.

1

3

e

1

3

al

sin −

rS

3.

√

· 1 (1 + 2 )−12 (2) − (1 + 2 )12 · 1

1 + 2

(1 + 2 )12

2

−

+ =

−

+ =−

+0

()2

(1 + 2 )−12 2 − (1 + 2 )

−1

1

=−

= √

=−

2

(1 + 2 )12 2

2 1 + 2

Fo

1.

in the ﬁgure correspond to = −5, 0, 5, and 10.

19.

21.

23.

25.

3

−2

(2 − 3) =

0 1

−2

2

0

3

3

3 − 3 −2 = (9 − 9) − − 8 + 6 =

3

1

+ 1 3 − = 10 5 +

4

(2 − 3)(42 + 1) =

0

4

2

1

2

0

205

1 4

16

− 1 2

2

0

−2

=0−

8

3

−

18

3

1

10 (−32)

= − 10

3

+

1

16 (16)

− 1 (4) = − − 16 + 1 − 2 =

2

5

21

5

2

(83 − 122 + 2 − 3) = 24 − 43 + 2 − 3 0 = (32 − 32 + 4 − 6) − 0 = −2

(4 sin − 3 cos ) = − 4 cos − 3 sin 0 = (4 − 0) − (−4 − 0) = 8

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

¤

206

27.

1

29.

CHAPTER 4

4

4 + 6

√

INTEGRALS

=

4

1

4

6

√ +√

=

4

1

4

(4−12 + 612 ) = 812 + 432 = (16 + 32) − (8 + 4) = 36

1

√ 4

√ √ 4 √

√

4

5 = 5 1 −12 = 5 2 = 5 (2 · 2 − 2 · 1) = 2 5

1

1

31.

4

4

4√

(1 + ) = 1 (12 + 32 ) = 2 32 + 2 52 = 16 +

3

5

3

1

1

33.

4

0

35.

64

1

64

5

4

−

2

4

1

cos2

+

=

(sec2 + 1)

2

2 cos cos

0

0

4

= tan + 0 = tan + − (0 + 0) = 1 +

4

4

4

1 + cos2

= cos2

3

+

2

5

=

14

3

256

15

if − 3 ≥ 0

−3

−( − 3)

Thus,

e

=

−3

if ≥ 3

+

5

9

−0 =1

rS

4

9

if − 3 0

3 − if 3

3

5

3

5

5

| − 3| = 2 (3 − ) + 3 ( − 3) = 3 − 1 2 2 + 1 2 − 3 3

2

2

2

= 9 − 9 − (6 − 2) + 25 − 15 − 9 − 9 = 5

2

2

2

2

Fo

39. | − 3| =

−1

=

al

1

94

1

√

1 54

1 √

95

4

45

5 + 5 4

= 0 (

+

37. 0

+ ) =

= 4 94 + 5 95 =

9

9

94

95 0

0

2

62

5

√

64

64

64

13

1+ 3

1

√

+ 12 =

(−12 + −16 )

−12 + (13) − (12) =

=

12

1

1

1

64

= 16 + 192 − 2 + 6 = 14 + 186 = 256

= 212 + 6 56

5

5

5

5

5

1

41.

+

0

2

2

0

2

[ − 2(−)] + 0 [ − 2()] = −1 3 + 0 (−) = 3 1 2 −1 − 1 2 0

2

2

= 3 0 − 1 − (2 − 0) = − 7 = −35

2

2

( − 2 ||) =

0

−1

ot

43. The graph shows that = 1 − 2 − 54 has -intercepts at

= ≈ −086 and at = ≈ 042. So the area of the region that

N

lies under the curve and above the -axis is

(1 − 2 − 54 ) = − 2 − 5

= ( − 2 − 5 ) − ( − 2 − 5 )

≈ 136

45. =

2

2

2 − 2 = 2 − 1 3 0 = 4 − 8 − 0 =

3

3

0

4

3

47. If 0 () is the rate of change of weight in pounds per year, then () represents the weight in pounds of the child at age . We

know from the Net Change Theorem that

10

5

0 () = (10) − (5), so the integral represents the increase in the child’s

weight (in pounds) between the ages of 5 and 10.

49. Since () is the rate at which oil leaks, we can write () = − 0 (), where () is the volume of oil at time . [Note that the

minus sign is needed because is decreasing, so 0 () is negative, but () is positive.] Thus, by the Net Change Theorem,

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

SECTION 4.4

120

0

() = −

120

0

INDEFINITE INTEGRALS AND THE NET CHANGE THEOREM

¤

207

0 () = − [ (120) − (0)] = (0) − (120), which is the number of gallons of oil that leaked

from the tank in the ﬁrst two hours (120 minutes).

5000

51. By the Net Change Theorem,

1000

0 () = (5000) − (1000), so it represents the increase in revenue when

production is increased from 1000 units to 5000 units.

53. In general, the unit of measurement for

() is the product of the unit for () and the unit for . Since () is

measured in newtons and is measured in meters, the units for abbreviated N·m.)

55. (a) Displacement =

3

0

(3 − 5) =

3

3

2

3

2 − 5 0 =

27

2

100

0

() are newton-meters. (A newton-meter is

− 15 = − 3 m

2

53

3

|3 − 5| = 0 (5 − 3) + 53 (3 − 5)

53

3

= 5 − 3 2 0 + 3 2 − 5 53 = 25 − 3 · 25 + 27 − 15 − 3 ·

2

2

3

2

9

2

2

(b) Distance traveled =

=

⇒ () = 1 2 + 4 +

2

10

0

500

3

0

25

3

=

41

6

m

10 1 2

+ 4 + 5 = 10 1 2 + 4 + 5 = 1 3 + 22 + 5 10

0

+ 200 + 50 =

4

−

⇒ (0) = = 5 ⇒ () = 1 2 + 4 + 5 ms

2

() =

2

0

416 2

3

2

6

0

m

4

√

4

9 + 2 = 9 + 4 32 = 36 +

3

0

Fo

59. Since 0 () = (), =

|()| =

25

9

al

57. (a) 0 () = () = + 4

e

0

rS

(b) Distance traveled =

0

61. Let be the position of the car. We know from Equation 2 that (100) − (0) =

100

0

32

3

−0 =

ot

1

180 (38

= 46 2 kg.

3

() . We use the Midpoint Rule for

0 ≤ ≤ 100 with = 5. Note that the length of each of the ﬁve time intervals is 20 seconds =

So the distance traveled is

100

1

() ≈ 180 [(10) + (30) + (50) + (70) + (90)] =

0

140

3

20

3600

+ 58 + 51 + 53 + 47) =

hour =

247

180

1

180

hour.

≈ 14 miles.

N

63. By the Net Change Theorem, the amount of water after four days is

25,000 +

4

0

() ≈ 25,000 + 4 = 25,000 +

4−0

4

[(05) + (15) + (25) + (35)]

≈ 25,000 + [1500 + 1770 + 740 + (−690)] = 28,320 liters

65. Power is the rate of change of energy with respect to time; that is, () = 0 (). By the Net Change Theorem and the

Midpoint Rule,

(24) − (0) =

24

0

() ≈

24 − 0

[ (1) + (3) + (5) + · · · + (21) + (23)]

12

≈ 2(16,900 + 16,400 + 17,000 + 19,800 + 20,700 + 21,200

+ 20,500 + 20,500 + 21,700 + 22,300 + 21,700 + 18,900)

= 2(237,600) = 475,200

Thus, the energy used on that day was approximately 4.75 × 105 megawatt-hours. c ° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

¤

208

67.

CHAPTER 4 INTEGRALS

(sin + sinh ) = − cos + cosh +

69.

2 + 1 +

1

2 + 1

0

√

1 3

2 − 1

=

4 − 1

=

71.

6

3

+ + tan−1 +

3

=

1

√

3

0

2 − 1

=

2 + 1)(2 − 1)

(

1

√

3

2

0

6

−0 =

√

1√3

1

= arctan 0

= arctan 1 3 − arctan 0

+1

4.5 The Substitution Rule

1. Let = . Then = and

1

= , so

, so

sin

=

1

(− cos )

1

+ = − cos + .

3 (−) = −

4

+ = − 1 cos4 + .

4

4

, so

sin(2 ) =

9. Let = 1 − 2. Then = −2 and = − 1 , so

2

(1 − 2)9 =

Fo

1

2

rS

cos3 sin =

7. Let = 2 . Then = 2 and =

√

1 32

1 2

2 3 + 1 =

+ = · 32 + = 2 (3 + 1)32 + .

1 =

3

9

3 32

3 3

5. Let = cos . Then = − sin and sin = −, so

1

al

1

3

sin =

e

3. Let = 3 + 1. Then = 32 and 2 =

9 − 1 = − 1 ·

2

2

1 10

10

sin 1 = − 1 cos + = − 1 cos(2 ) + .

2

2

2

1

+ = − 20 (1 − 2)10 + .

11. Let = 2 + 2 . Then = (2 + 2) = 2(1 + ) and ( + 1) =

1

2

, so

N

ot

√

32

1 32

( + 1) 2 + 2 =

+ = 1 2 + 2

1 =

+ .

2

3

2 32

√

Or: Let = 2 + 2 . Then 2 = 2 + 2 ⇒ 2 = (2 + 2) ⇒ = (1 + ) , so

√

( + 1) 2 + 2 = · = 2 = 1 3 + = 1 (2 + 2 )32 + .

3

3

13. Let = 3. Then = 3 and =

1

3

, so sec 3 tan 3 = sec tan 1 =

3

1

3

sec + =

1

3

sec 3 + .

15. Let = 3 + 3 . Then = (3 + 32 ) = 3( + 2 ) , so

+ 2

√

=

3 + 3

1

3

12

=

1

3

17. Let = tan . Then = sec2 , so

−12 =

(2 + 1)(3 + 3)4 =

· 212 + =

sec2 tan3 =

19. Let = 3 + 3. Then = (32 + 3) and

1

3

4 ( 1 ) =

3

1

3

1

3

2

3

3 + 3 + .

3 = 1 4 + =

4

1

4

tan4 + .

= (2 + 1) , so

· 1 5 + =

5

1

(3

15

+ 3)5 + .

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

SECTION 4.5 THE SUBSTITUTION RULE

21. Let = sin . Then = cos , so

cos

= sin2

1

=

2

−2 =

[or −csc + ].

23. Let = 1 + 3 . Then = 3 2 and 2 =

2

√

=

3

1 + 3

−13

1

3

=

1

3

1

3

1

1

−1

+ =− + =−

+

−1

sin

, so

· 3 23 + = 1 (1 + 3 )23 + .

2

2

25. Let = cot . Then = − csc2 and csc2 = −, so

√

√

32

+ = − 2 (cot )32 + . cot csc2 =

(−) = −

3

32

27. Let = sec . Then = sec tan , so

sec2 (sec tan ) =

29. Let = 2 + 5. Then = 2 and =

(2 + 5)8 =

− 5), so

9

1

( − 5)8 ( 1 ) = 1 ( − 58 )

2

2

4

1

(

2

1

= 1 ( 10 10 − 5 9 ) + =

4

9

31. () = (2 − 1)3 .

2 = 1 3 + =

3

1

40 (2

1

3

sec3 + .

+ 5)10 −

5

36 (2

+ 5)9 +

rS

e

sec3 tan =

al

= 2 − 1 ⇒ = 2 so

(2 − 1)3 =

3

1

2

= 1 4 + = 1 (2 − 1)4 +

8

8

Fo

Where is positive (negative), is increasing (decreasing). Where

changes from negative to positive (positive to negative), has a local minimum (maximum).

⇒ = cos , so

ot

33. () = sin3 cos . = sin

sin3 cos =

2,

3 = 1 4 + =

4

1

4

sin4 +

changes from positive to negative and has a local

N

Note that at =

maximum. Also, both and are periodic with period , so at = 0 and at = , changes from negative to positive and has local minima.

35. Let =

,

2

so =

1

0

2

. When = 0, = 0; when = 1, =

cos(2) =

2

cos

0

2

=

2

.

2

Thus,

[sin ]2 =

0

2

sin − sin 0 =

2

2

(1

− 0) =

2

3

28 (16

− 1) =

45

28

37. Let = 1 + 7, so = 7 . When = 0, = 1; when = 1, = 8. Thus,

1

√

3

1 + 7 =

0

1

39. Let = 4, so =

0

sec2 (4) =

1

4

4

0

8

13 ( 1 ) =

7

1

7

3 43

4

8

1

=

43

3

28 (8

¤

− 143 ) =

. When = 0, = 0; when = , = 4. Thus,

4

sec2 (4 ) = 4 tan 0 = 4 tan − tan 0 = 4(1 − 0) = 4.

4

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

209

¤

210

41.

CHAPTER 4 INTEGRALS

4

−4

(3 + 4 tan ) = 0 by Theorem 6(b), since () = 3 + 4 tan is an odd function.

43. Let = 1 + 2, so = 2 . When = 0, = 1; when = 13, = 27. Thus,

13

=

3

(1 + 2)2

0

27

−23

1

1

2

27

= 1 · 313

= 3 (3 − 1) = 3.

2

2

1

45. Let = 2 + 2 , so = 2 and =

2 + 2 =

22

12

2

0

1

2

1

2

. When = 0, = 2 ; when = , = 22 . Thus,

22

22

√

= 1 2 32

= 1 32

= 1 (22 )32 − (2 )32 = 1 2 2 − 1 3

2 3

3

3

3

2

2

47. Let = − 1, so + 1 = and = . When = 1, = 0; when = 2, = 1. Thus,

1

√

− 1 =

1

0

1

1

√

( + 1) =

(32 + 12 ) = 2 52 + 2 32 =

5

3

0

0

49. Let = −2 , so = −2−3 . When =

1

12

cos(−2 )

=

3

51. Let = 1 +

1

cos

4

√

, so =

2

−2

=

1

2

1

,

2

2

3

=

16

15 .

cos =

1

4

1

1 sin 1 = (sin 4 − sin 1).

2

2

√

1

√ ⇒ 2 = ⇒ 2( − 1) = . When = 0, = 1; when = 1,

2

2

1

1

1

1

1

· [2( − 1) ] = 2

− 4 = 2 − 2 + 3

4

3

2

3 1

1

1

1

1

1 1

1

= 2 − 8 + 24 − − 2 + 1 = 2 12 = 6

3

√

=

(1 + )4

2

Fo

0

1

+

= 4; when = 1, = 1. Thus,

4

= 2. Thus,

2

5

e

al

2

rS

53. From the graph, it appears that the area under the curve is about

ot

1 + a little more than 1 · 1 · 07 , or about 14. The exact area is given by

2

1√

= 0 2 + 1 . Let = 2 + 1, so = 2 . The limits change to

N

2 · 0 + 1 = 1 and 2 · 1 + 1 = 3, and

3

√

√

3√

= 1 1 = 1 2 32 = 1 3 3 − 1 = 3 −

2

2 3

3

1

1

3

≈ 1399.

55. First write the integral as a sum of two integrals:

2

√

2 √

2 √

( + 3) 4 − 2 = 1 + 2 = −2 4 − 2 + −2 3 4 − 2 . 1 = 0 by Theorem 6(b), since

√

() = 4 − 2 is an odd function and we are integrating from = −2 to = 2. We interpret 2 as three times the area of

a semicircle with radius 2, so = 0 + 3 · 1 · 22 = 6.

2

=

−2

57. The volume of inhaled air in the lungs at time is

() =

0

() =

0

25

5

=

− cos 0

4

25

1

1

2

5

sin

= sin

substitute =

2

5

2

2

0

5

2

5

2

=

− cos

+1 =

1 − cos

liters

4

5

4

5

2

,

5

=

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

2

5

SECTION 4.5 THE SUBSTITUTION RULE

59. Let = 2. Then = 2 , so

2

0

(2) =

61. Let = −. Then = −, so

(−) =

−

−

()(−) =

−

−

4

0

() 1 =

2

() =

−

−

1

2

4

0

¤

211

() = 1 (10) = 5.

2

()

From the diagram, we see that the equality follows from the fact that we are reﬂecting the graph of , and the limits of integration, about the -axis.

63. Let = 1 − . Then = 1 − and = −, so

1

0

65.

(1 − ) =

2

0

0

1

(1 − ) (−) =

1

0

(1 − ) =

1

0

(1 − ) .

2

sin 2 −

= − , = −

2

0

2

2

0

= 2 (sin )(−) = 0 (sin ) = 0 (sin )

(cos ) =

=

5 − 3

1 1

− 3 = − 1 ln || + = − 1 ln |5 − 3| + .

3

3

69. Let = ln . Then =

, so

rS

al

67. Let = 5 − 3. Then = −3 and = − 1 , so

3

e

Continuity of is needed in order to apply the substitution rule for deﬁnite integrals.

(ln )2

= 2 = 1 3 + = 1 (ln )3 + .

3

3

71. Let = 1 + . Then = , so

√

√

1 + =

= 2 32 + = 2 (1 + )32 + .

3

3

Fo

√

Or: Let = 1 + . Then 2 = 1 + and 2 = , so

√

1 + = · 2 = 2 3 + = 2 (1 + )32 + .

3

3

73. Let = tan . Then = sec2 , so

77.

= + = tan + .

1

1

2

+

= tan−1 +

= tan−1 + 1 ln|| +

2

1 + 2

1 + 2

= tan−1 + 1 ln1 + 2 + = tan−1 + 1 ln 1 + 2 + [since 1 + 2 0].

1+

=

1 + 2

N

tan sec2 =

ot

75. Let = 1 + 2 . Then = 2 , so

2

2

sin 2 sin cos

= 2

= 2. Let = cos . Then = − sin , so

1 + cos2

1 + cos2

= −2 · 1 ln(1 + 2 ) + = − ln(1 + 2 ) + = − ln(1 + cos2 ) + .

2 = −2

2

1 + 2

Or: Let = 1 + cos2 .

1

cos

. Let = sin . Then = cos , so cot =

= ln || + = ln |sin | + . cot =

79.

sin

. When = , = 1; when = 4 ; = 4. Thus,

4

4

=

−12 = 2 12 = 2(2 − 1) = 2.

81. Let = ln , so =

4

√

ln

1

1

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

¤

212

CHAPTER 4 INTEGRALS

83. Let = + , so = ( + 1) . When = 0, = 1; when = 1, = + 1. Thus,

1

0

85.

+ 1

=

+

+1

1

+1

1

= ln | + 1| − ln |1| = ln( + 1).

= ln ||

1

sin

sin

. By Exercise 64,

= (sin ), where () =

=·

1 + cos2

2 − 2

2 − sin2

sin sin

=

(sin ) =

(sin ) =

2

2 0

2 0 1 + cos2

0 1 + cos

0

Let = cos . Then = − sin . When = , = −1 and when = 0, = 1. So

1

1

sin

−1

=

=

= − tan−1 −1

2 0 1 + cos2

2 1 1 + 2

2 −1 1 + 2

2

2

[tan−1 1 − tan−1 (−1)] =

− −

=

2

2 4

4

4

e

=

=1

rS

1. (a)

al

4 Review

(∗ ) ∆ is an expression for a Riemann sum of a function .

∗ is a point in the th subinterval [−1 ] and ∆ is the length of the subintervals.

Fo

(b) See Figure 1 in Section 4.2.

(c) In Section 4.2, see Figure 3 and the paragraph beside it.

2. (a) See Deﬁnition 4.2.2.

ot

(b) See Figure 2 in Section 4.2.

(c) In Section 4.2, see Figure 4 and the paragraph by it (contains “net area”).

N

3. See the Fundamental Theorem of Calculus on page 317.

4. (a) See the Net Change Theorem on page 324.

(b)

5. (a)

(b)

(c)

6. (a)

2

1

() represents the change in the amount of water in the reservoir between time 1 and time 2 .

120

60

120

60

120

60

() represents the change in position of the particle from = 60 to = 120 seconds.

|()| represents the total distance traveled by the particle from = 60 to 120 seconds.

() represents the change in the velocity of the particle from = 60 to = 120 seconds.

() is the family of functions { | 0 = }. Any two such functions differ by a constant.

(b) The connection is given by the Net Change Theorem:

() =

() if is continuous.

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

CHAPTER 4 REVIEW

¤

213

7. The precise version of this statement is given by the Fundamental Theorem of Calculus. See the statement of this theorem and

the paragraph that follows it at the end of Section 4.3.

8. See the Substitution Rule (4.5.4). This says that it is permissible to operate with the after an integral sign as if it were a

differential.

1. True by Property 2 of the Integral in Section 4.2.

3. True by Property 3 of the Integral in Section 4.2.

For example, let () = 2 . Then

1√

1

1 2

2 = 0 = 1 , but

= 1 =

2

3

0

0

7. True by Comparison Property 7 of the Integral in Section 4.2.

The integrand is an odd function that is continuous on [−1 1], so the result follows from Theorem 4.5.6(b).

al

9. True.

1

√ .

3

e

5. False.

11. False.

For example, the function = || is continuous on R, but has no derivative at = 0.

13. True.

By Property 5 in Section 4.2,

sin

=

3

[by reversing limits].

15. False.

rS

2

3

Fo

2

3 sin sin sin

=

+

⇒

2

3

2

3

2 sin sin sin sin sin

−

⇒

=

+

2

3

() is a constant, so

() = 0, not () [unless () = 0]. Compare the given statement

17. False.

ot

carefully with FTC1, in which the upper limit in the integral is .

The function () = 14 is not bounded on the interval [−2 1]. It has an inﬁnite discontinuity at = 0, so it is

N

not integrable on the interval. (If the integral were to exist, a positive value would be expected, by Comparison

Property 6 of Integrals.)

1. (a)

6 =

6

=1

(−1 ) ∆

[∆ =

6−0

6

= 1]

= (0 ) · 1 + (1 ) · 1 + (2 ) · 1 + (3 ) · 1 + (4 ) · 1 + (5 ) · 1

≈ 2 + 35 + 4 + 2 + (−1) + (−25) = 8

The Riemann sum represents the sum of the areas of the four rectangles above the -axis minus the sum of the areas of the two rectangles below the

-axis.

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

¤

214

CHAPTER 4 INTEGRALS

(b)

6 =

6

[∆ =

( ) ∆

=1

6−0

6

= 1]

= (1 ) · 1 + (2 ) · 1 + (3 ) · 1 + (4 ) · 1 + (5 ) · 1 + (6 ) · 1

= (05) + (15) + (25) + (35) + (45) + (55)

≈ 3 + 39 + 34 + 03 + (−2) + (−29) = 57

The Riemann sum represents the sum of the areas of the four rectangles above the -axis minus the sum of the areas of the two rectangles below the

-axis.

√

1√

1

1

3. 0 + 1 − 2 = 0 + 0 1 − 2 = 1 + 2 .

1 can be interpreted as the area of the triangle shown in the ﬁgure

6

0

() =

4

0

() +

6

4

+ .

4

() ⇒ 10 = 7 +

7. First note that either or must be the graph of

13.

0

() , since

6

4

() = 10 − 7 = 3

0

() = 0, and (0) 6= 0. Now notice that 0 when

is increasing, and that 0 when is increasing. It follows that is the graph of (), is the graph of 0 (), and is the

graph of 0 () .

2

2

2 3

8 + 32 = 8 · 1 4 + 3 · 1 3 1 = 24 + 3 1 = 2 · 24 + 23 − (2 + 1) = 40 − 3 = 37

4

3

1

1

1 − 9 = −

0

9

1

1 10 1

10

0

= 1−

1

10

0

N

1

−0 =

9

10

√

9

9

− 22

=

(−12 − 2) = 212 − 2 = (6 − 81) − (2 − 1) = −76

1

1

15. Let = 2 + 1, so = 2 and =

17.

() ⇒

Fo

11.

0

4

ot

9.

6

rS

5.

1

2

al

Area = 1 (1)(1) + 1 ()(1)2 =

2

4

e

and 2 can be interpreted as the area of the quarter-circle.

( 2 + 1)5 =

5

1

2

1

1

2

. When = 0, = 1; when = 1, = 2. Thus,

2

5 1 = 1 1 6 1 =

2

2 6

1

(64

12

− 1) =

63

12

=

21

.

4

1

does not exist because the function () = has an inﬁnite discontinuity at = 4;

( − 4)2

( − 4)2

that is, is discontinuous on the interval [1 5].

19. Let = 3 , so = 3 2 . When = 0, = 0; when = 1, = 1. Thus,

1

0

21.

2 cos( 3 ) =

4

−4

1

0

cos

1

3

1

= 1 sin 0 = 1 (sin 1 − 0) =

3

3

1

3

sin 1.

4 tan

4 tan

= 0 by Theorem 4.5.6(b), since () = is an odd function.

2 + cos

2 + cos

23. Let = sin . Then = cos , so

sin cos =

1

=

1

· 1 2 + =

2

1

(sin )2

2

+ .

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

CHAPTER 4 REVIEW

¤

215

25. Let = 2. Then = 2 , so

8

0

sec 2 tan 2 =

4

0

sec tan

4

√

= 1 sec 0 = 1 sec − sec 0 = 1 2 − 1 =

2

2

4

2

1

2

1

2

√

2 − 1.

2

27. Since 2 − 4 0 for 0 ≤ 2 and 2 − 4 0 for 2 ≤ 3, we have 2 − 4 = −(2 − 4) = 4 − 2 for 0 ≤ 2 and

2

− 4 = 2 − 4 for 2 ≤ 3. Thus,

2 3

3

2

3

3

2

3

− 4 =

− 4

(4 − 2 ) +

(2 − 4) = 4 −

+

3 0

3

0

0

2

2

8

16

8

16

32

= 8 − 3 − 0 + (9 − 12) − 3 − 8 = 3 − 3 + 3 = 3 − 9 = 23

3

3

29. Let = 1 + sin . Then = cos , so

√

cos

√

= −12 = 212 + = 2 1 + sin + .

1 + sin

al

e

31. From the graph, it appears that the area under the curve =

√

between = 0

rS

and = 4 is somewhat less than half the area of an 8 × 4 rectangle, so perhaps about 13 or 14. To ﬁnd the exact value, we evaluate

4

4 √

4

= 0 32 = 2 52 = 2 (4)52 =

5

5

0

33. () =

0

64

5

= 128.

Fo

0

2

⇒ 0 () =

1 + 3

0

2

2

=

3

1+

1 + 3

= 43 . Also,

=

, so

4

= cos(2 )

= 43 cos(8 ). cos(2 ) = cos(2 ) ·

0 () =

0

0

ot

35. Let = 4 . Then

1

√ cos cos cos cos cos

37. = √

=

+ √

=

−

1

1

1

√

√

cos cos 1

2 cos − cos

0

√ =

=

− √

2

2

N

⇒

√

√

√

√

√

12 + 3 ≤ 2 + 3 ≤ 32 + 3 ⇒ 2 ≤ 2 + 3 ≤ 2 3, so

√

√

3√

3√

2(3 − 1) ≤ 1 2 + 3 ≤ 2 3(3 − 1); that is, 4 ≤ 1 2 + 3 ≤ 4 3.

39. If 1 ≤ ≤ 3, then

41. 0 ≤ ≤ 1

⇒ 0 ≤ cos ≤ 1 ⇒ 2 cos ≤ 2

43. ∆ = (3 − 0)6 =

1

,

2

⇒

1

0

2 cos ≤

1

0

2 =

1

3

3 1

0=

1

3

so the endpoints are 0, 1 , 1, 3 , 2, 5 , and 3, and the midpoints are 1 , 3 , 5 , 7 , 9 , and

2

2

2

4 4 4 4 4

[Property 7].

11

.

4

The Midpoint Rule gives

3

0

sin(3 ) ≈

6

=1

( ) ∆ =

1

2

3

3

3

3

3

3

sin 1 + sin 3 + sin 5 + sin 7 + sin 9 + sin 11

≈ 0280981.

4

4

4

4

4

4

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

¤

216

CHAPTER 4 INTEGRALS

45. Note that () = 0 (), where () = the number of barrels of oil consumed up to time . So, by the Net Change Theorem,

8

0

() = (8) − (0) represents the number of barrels of oil consumed from Jan. 1, 2000, through Jan. 1, 2008.

47. We use the Midpoint Rule with = 6 and ∆ =

24

0

= 4. The increase in the bee population was

24 − 0

6

() ≈ 6 = 4[(2) + (6) + (10) + (14) + (18) + (22)]

≈ 4[50 + 1000 + 7000 + 8550 + 1350 + 150] = 4(18,100) = 72,400

49. Let = 2 sin . Then = 2 cos and when = 0, = 0; when =

() = sin +

0

0

() 1 −

1

1 + 2

2

0

() 1 =

2

1

2

2

0

() =

1

2

2

0

() = 1 (6) = 3.

2

()

()

⇒ () = cos + sin +

[by differentiation] ⇒

1 + 2

1 + 2

2

1 + 2

( cos + sin )

= cos + sin ⇒ ()

= cos + sin ⇒ () =

2

1+

2

53. Let = () and = 0 () . So 2

1

0

() 0 () = 2

(1 − ) =

0

1

()

()

()

= 2 () = [ ()]2 − [ ()]2 .

()(−) =

1

0

() =

1

0

() .

N

ot

Fo

55. Let = 1 − . Then = −, so

e

51.

(2 sin ) cos =

al

0

= 2. Thus,

rS

2

,

2

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

PROBLEMS PLUS

1. Differentiating both sides of the equation sin =

2

0

() (using FTC1 and the Chain Rule for the right side) gives

sin + cos = 2 (2 ). Letting = 2 so that (2 ) = (4), we obtain sin 2 + 2 cos 2 = 4 (4), so

(4) = 1 (0 + 2 · 1) =

4

.

2

3. Differentiating the given equation,

0

() = [ ()]2 , using FTC1 gives () = 2 () 0 () ⇒

()[2 0 () − 1] = 0, so () = 0 or 0 () = 1 . Since () is never 0, we must have 0 () =

2

() = 1 + . To ﬁnd , we substitute into the given equation to get

2

0

2

2

+ = 1 +

2

1

2

⇒

⇔

()

cos

[1 + sin(2 )] . Using FTC1 and the Chain Rule (twice) we have

0

rS

0

1

√

, where () =

1 + 3

e

+ = 1 2 + + 2 . It follows that 2 = 0, so = 0, and () = 1 .

4

2

5. () =

1

1

0 () =

[1 + sin(cos2 )](− sin ). Now =

0 () =

2

3

3

1 + [()]

1 + [()]

2

0

[1 + sin(2 )] = 0, so

0

1

= √

(1 + sin 0)(−1) = 1 · 1 · (−1) = −1.

1+0

Fo

0

and 0 () =

al

1 2

4

1

1

2

7. () = 2 + − 2 = (− + 2)( + 1) = 0

else. The integral

⇔ = 2 or = −1. () ≥ 0 for ∈ [−1 2] and () 0 everywhere

(2 + − 2 ) has a maximum on the interval where the integrand is positive, which is [−1 2]. So

ot

= −1, = 2. (Any larger interval gives a smaller integral since () 0 outside [−1 2]. Any smaller interval also gives a smaller integral since () ≥ 0 in [−1 2].)

0

[[]] into the sum

N

9. (a) We can split the integral

=1

−1

[[]] . But on each of the intervals [ − 1 ) of integration,

[[]] is a constant function, namely − 1. So the ith integral in the sum is equal to ( − 1)[ − ( − 1)] = ( − 1). So the original integral is equal to

( − 1) =

=1

(b) We can write

Now

0

[[]] =

[[]] =

[[]]

0

0

[[]] −

[[]] +

[ ]

[]

−1

=

=1

0

( − 1)

.

2

[[]] .

[[]] . The ﬁrst of these integrals is equal to 1 ([[]] − 1) [[]],

2

by part (a), and since [[]] = [[]] on [[[]] ], the second integral is just [[]] ( − [[]]). So

0

[[]] = 1 ([[]] − 1) [[]] + [[]] ( − [[]]) =

2

Therefore,

[[]] =

1

2

[[]] (2 − [[]] − 1) −

1

2

1

2

[[]] (2 − [[]] − 1) and similarly

[[]] (2 − [[]] − 1).

0

[[]] =

1

2

[[]] (2 − [[]] − 1).

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

217

218

¤

CHAPTER 4 PROBLEMS PLUS

11. Let () =

() = + 2 + 3 + 4 = + 2 + 3 + 4 . Then (0) = 0, and (1) = 0 by the

2

3

4

2

3

4

0

0

given condition, +

+ + = 0. Also, 0 () = () = + + 2 + 3 by FTC1. By Rolle’s Theorem, applied to

2 3 4

on [0 1], there is a number in (0 1) such that 0 () = 0, that is, such that () = 0. Thus, the equation () = 0 has a root between 0 and 1.

More generally, if () = 0 + 1 + 2 2 + · · · + and if 0 +

1

2

+

+ ··· +

= 0 then the equation

2

3

+1

() = 0 has a root between 0 and 1 The proof is the same as before:

1 2 2 3

() = 0 +

Let () =

+

+ ··· +

. Then (0) = (1) = 0 and 0 () = (). By

2

3

+1

0

Rolle’s Theorem applied to on [0 1], there is a number in (0 1) such that 0 () = 0, that is, such that () = 0.

0

0

() =

0

()( − ) =

()( − ) =

() −

()

0

0

= 0 () + () − () = 0 ()

0

0

() + . Setting = 0 gives = 0.

Fo

1

1

1

+√ √

+··· + √ √

√ √

+

+1

+2

1

= lim

+

+ ··· +

→∞

+1

+2

+

1

1

1

1

+

+··· + √

= lim

→∞

1+1

1 + 1

1 + 2

ot

→∞

0

1

→∞

=1

= lim

N

15. lim

() by FTC1, while

0

Hence,

e

al

rS

13. Note that

=

0

1

1 where () = √

1+

√

√

1

1

√

= 2 1 + 0 = 2 2 − 1

1+

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

5

APPLICATIONS OF INTEGRATION

5.1 Areas Between Curves

=0

5. =

2

3

−

2

−1

=

( − ) =

2

−1

1

3

+ 1 − (0) =

4

0

=1

=0

=

1

0

(5 − 2 ) − =

0

4

4

(4 − 2 ) = 22 − 1 3 0 = 32 −

3

(8 − − 2 )

= 22 − 3 +

1

2

=

1

2

− (0) =

32

3

0

(9 − 2 ) − ( + 1)

2

3

2

−

= 8 −

2

3 −1

8

= 16 − 2 − 3 − −8 −

1

1

− ( 2 − 1) =

( 12 − 2 + 1) = 2 32 − 1 3 +

3

3

0

4

3

64

3

e

3. =

( − ) =

=4

+

1

3

39

2

⇔ 2 − 4 + 4 = ⇔ 2 − 5 + 4 = 0 ⇔

Fo

7. The curves intersect when ( − 2)2 =

al

rS

1. =

( − 1)( − 4) = 0 ⇔ = 1 or 4.

=

1

4

[ − ( − 2)2 ] =

4

1

(−2 + 5 − 4)

=

9

2

N

ot

4

= − 1 3 + 5 2 − 4 1

3

2

= − 64 + 40 − 16 − − 1 +

3

3

9. First ﬁnd the points of intersection:

5

2

−4

√

+3

+3 =

2

⇒

√

2

+3 =

+3

2

2

⇒ + 3 = 1 ( + 3)2

4

⇒

4( + 3) − ( + 3)2 = 0 ⇒ ( + 3)[4 − ( + 3)] = 0 ⇒ ( + 3)(1 − ) = 0 ⇒ = −3 or 1. So

1

√

+3

=

+3−

2

−3

1

( + 3)2

= 2 ( + 3)32 −

3

4

−3

16

4

= 3 − 4 − (0 − 0) = 3

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

219

220

¤

CHAPTER 5 APPLICATIONS OF INTEGRATION

11. The curves intersect when 1 − 2 = 2 − 1

=

=

⇔ 2 = 1 ⇔ = ±1.

(1 − 2 ) − (2 − 1)

1

−1

⇔ 2 = 22

1

2(1 − 2 )

−1

=2·2

1

0

(1 − 2 )

1

= 4 − 1 3 0 = 4 1 − 1 =

3

3

13. 12 − 2 = 2 − 6

8

3

⇔ 22 = 18 ⇔

2 = 9 ⇔ = ±3, so

3

(12 − 2 ) − (2 − 6)

=

0

18 − 22

[by symmetry]

3

= 2 18 − 2 3 0 = 2 [(54 − 18) − 0]

3

= 2(36) = 72

for 0 . By symmetry,

2

3

(8 cos − sec2 )

= 2

=

3

0

⇒ 8 cos3 = 1 ⇒ cos3 =

Fo

15. The curves intersect when 8 cos = sec2

al

3

rS

=2

e

−3

1

8

⇒ cos =

1

2

⇒

ot

3

= 2 8 sin − tan 0

√

√

√

= 2 8 · 23 − 3 = 2 3 3

N

√

3

=6

17. 2 2 = 4 + 2

=

2

−2

=2

(4 + 2 ) − 2 2

2

0

⇔ 2 = 4 ⇔ = ±2, so

(4 − 2 )

[by symmetry]

2

= 2 4 − 1 3 0 = 2 8 − 8 =

3

3

32

3

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

SECTION 5.1 AREAS BETWEEN CURVES

19. By inspection, the curves intersect at = ± 1 .

2

=

12

[cos − (42 − 1)]

−12

=2

12

0

(cos − 42 + 1) [by symmetry]

12

1

1

= 2 sin − 4 3 + 0 = 2 −

3

1

2

=2 +1 = +2

3

3

1

6

+

1

2

−0

21. From the graph, we see that the curves intersect at = 0, =

,

2

and = . By symmetry,

2

2

2

2

cos − 1 − 2 = 2

= 2

cos − 1 − cos − 1 +

0

0

0

2

2

1

1

= 2 sin − + 2 0 = 2 1 − + · − 0 = 2 1 − + = 2 −

2

4

2

4

2

Fo

rS

al

e

=

23. Notice that cos = sin 2 = 2 sin cos

=

6

(cos − sin 2) +

0

=

25.

or

.

2

2

6

(sin 2 − cos )

6

2

cos 2 0 + − 1 cos 2 − sin 6

2

− 0 + 1 · 1 + 1 − 1 − −1 · 1 − 1 =

2

2

2 2

2

N

= sin +

6

ot

2 sin = 1 or cos = 0 ⇔ =

⇔ 2 sin cos − cos = 0 ⇔ cos (2 sin − 1) = 0 ⇔

1

2

+

1

2

1

2

1

2

·

1

2

√

= ⇒ 1 2 = ⇒ 2 − 4 = 0 ⇒ ( − 4) = 0 ⇒ = 0 or 4, so

4

4

9

√

1

√

=

− 1 +

−

2

2

1

2

0

=

=

=

4

2 32

3

16

3

81

4

+

4

+

− 26 =

59

12

− 1 2

4

0

1 2

4

− 2 32

3

9

4

− 4 − 0 + 81 − 18 − 4 −

4

32

3

16

3

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

¤

221

222

¤

CHAPTER 5 APPLICATIONS OF INTEGRATION

27. Graph the three functions = 12 , = , and =

1

8 ;

2

1

1

1

−

− +

8

2

8

0

1

1 7

2 −2 1

= 0 8 + 1 − 8

1

2

1

7 2

1

+ − − 2

=

16

16

0

1

1

7

1

1

= 16 + − 2 − 4 − −1 − 16 = 3

4

=

1

29. An equation of the line through (0 0) and (3 1) is =

then determine the points of intersection: (0 0), (1 1), and 2 1 .

4

1

;

3

through (0 0) and (1 2) is = 2;

through (3 1) and (1 2) is = − 1 + 5 .

2

2

3

1

1

2 − 1 +

− 2 + 5 − 1

=

3

2

3

=

=

5

3

+

1

2 0

6

5

− 6 + 5

2

5

3

+ − 12 2 + 5 1

2

5

+ − 15 + 15 − − 12 + 5 =

4

2

2

5

5

6

1

3

al

0

5

2

31. The curves intersect when sin = cos 2

(on [0 2]) ⇔ sin = 1 − 2 sin2 ⇔ 2 sin2 + sin − 1 = 0 ⇔

2

|sin − cos 2|

0

6

=

=

=

33.

1

2

1 √

3+

4

3

2

6

sin 2 + cos

√

3−1

1

2

0

⇒ =

6.

2

6

(sin − cos 2)

ot

0

(cos 2 − sin ) +

+ − cos −

1

2

2 sin 2 6

√

√

3 − (0 + 1) + (0 − 0) − − 1 3 −

2

N

=

1

2

Fo

(2 sin − 1)(sin + 1) = 0 ⇒ sin =

=

rS

=

1

1

e

0

1

4

√

3

From the graph, we see that the curves intersect at = 0 and = ≈ 0896, with

sin(2 ) 4 on (0 ). So the area of the region bounded by the curves is

=

sin(2 ) − 4 = − 1 cos(2 ) − 1 5 0

2

5

0

= − 1 cos(2 ) − 1 5 +

2

5

1

2

≈ 0037

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

SECTION 5.1 AREAS BETWEEN CURVES

¤

From the graph, we see that the curves intersect at

35.

= ≈ −111 = ≈ 125 and = ≈ 286 with

3 − 3 + 4 32 − 2 on ( ) and 32 − 2 3 − 3 + 4 on ( ). So the area of the region bounded by the curves is

=

=

=

4

(3 − 32 − + 4) +

2

(3 − 2) − (3 − 3 + 4)

(−3 + 32 + − 4)

4 − 3 − 1 2 + 4 + − 1 4 + 3 + 1 2 − 4 ≈ 838

2

4

2

Graph Y1 =2/(1+xˆ4) and Y2 =xˆ2. We see that Y1 Y2 on (−1 1), so the

1

2

area is given by

− 2 . Evaluate the integral with a

1 + 4

−1

al

e

37.

1

3

( − 3 + 4) − (32 − 2) +

command such as fnInt(Y1 -Y2 ,x,-1,1) to get 280123 to ﬁve decimal places. rS

Another method: Graph () = Y1 =2/(1+xˆ4)-xˆ2 and from the graph

evaluate () from −1 to 1.

The curves intersect at = 0 and = ≈ 0749363.

√

− tan2 ≈ 025142

=

Fo

39.

ot

0

41. As the ﬁgure illustrates, the curves = and = 5 − 63 + 4

N

enclose a four-part region symmetric about the origin (since

5 − 63 + 4 and are odd functions of ). The curves intersect at values of where 5 − 63 + 4 = ; that is, where

(4 − 62 + 3) = 0. That happens at = 0 and where

√

√

√

√

√

√

36 − 12

=

= 3 ± 6; that is, at = − 3 + 6, − 3 − 6, 0, 3 − 6, and 3 + 6. The exact area is

2

√3+√6

√3+√6

5

5

( − 63 + 4) − = 2

− 63 + 3

2

2

6±

0

0

=2

√3−√6

0

√3+√6

( − 6 + 3) + 2 √ √ (−5 + 63 − 3)

5

3

3− 6

√

= 12 6 − 9

CAS

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

223

224

¤

CHAPTER 5 APPLICATIONS OF INTEGRATION

43. 1 second =

∆ =

hour, so 10 s =

1

3600

1360−0

5

=

1

,

1800

1

360

h. With the given data, we can take = 5 to use the Midpoint Rule.

so

distance Kelly − distance Chris =

1360

0

≈ 5 =

−

1

1800

1360

0

=

1360

0

( − )

[( − )(1) + ( − )(3) + ( − )(5)

+ ( − )(7) + ( − )(9)]

=

1

1800 [(22

=

1

1800 (2

− 20) + (52 − 46) + (71 − 62) + (86 − 75) + (98 − 86)]

+ 6 + 9 + 11 + 12) =

1

1800 (40)

=

1

45

mile, or 117 1 feet

3

45. Let () denote the height of the wing at cm from the left end.

200 − 0

[(20) + (60) + (100) + (140) + (180)]

5

e

≈ 5 =

() = (), where () is the velocity of car A

and A is its displacement. Similarly, the area under curve between = 0 and = is 0 B () = B ().

0

rS

47. We know that the area under curve between = 0 and = is

al

= 40(203 + 290 + 273 + 205 + 87) = 40(1058) = 4232 cm2

(a) After one minute, the area under curve is greater than the area under curve . So car A is ahead after one minute.

(b) The area of the shaded region has numerical value A (1) − B (1), which is the distance by which A is ahead of B after

Fo

1 minute.

(c) After two minutes, car B is traveling faster than car A and has gained some ground, but the area under curve from = 0 to = 2 is still greater than the corresponding area for curve , so car A is still ahead.

(d) From the graph, it appears that the area between curves and for 0 ≤ ≤ 1 (when car A is going faster), which

ot

corresponds to the distance by which car A is ahead, seems to be about 3 squares. Therefore, the cars will be side by side at the time where the area between the curves for 1 ≤ ≤ (when car B is going faster) is the same as the area for

49.

N

0 ≤ ≤ 1. From the graph, it appears that this time is ≈ 22. So the cars are side by side when ≈ 22 minutes.

To graph this function, we must ﬁrst express it as a combination of explicit

√

functions of ; namely, = ± + 3. We can see from the graph that the loop extends from = −3 to = 0, and that by symmetry, the area we seek is just twice the area under the top half of the curve on this interval, the equation of the

0

√

√

top half being = − + 3. So the area is = 2 −3 − + 3 . We

substitute = + 3, so = and the limits change to 0 and 3, and we get

3

3

√

= −2 0 [( − 3) ] = −2 0 (32 − 312 )

3

√

√

= −2 2 52 − 232 = −2 2 32 3 − 2 3 3 =

5

5

0

24

5

√

3

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

SECTION 5.1 AREAS BETWEEN CURVES

¤

By the symmetry of the problem, we consider only the ﬁrst quadrant, where

= 2 ⇒ = . We are looking for a number such that

4

4

=

⇒ 2 32 = 2 32

⇒

3

3

51.

0

32

0

32

=4

32

32

−

⇒ 2

32

=8 ⇒

= 4 ⇒ = 423 ≈ 252.

53. We ﬁrst assume that 0, since can be replaced by − in both equations without changing the graphs, and if = 0 the

curves do not enclose a region. We see from the graph that the enclosed area lies between = − and = , and by symmetry, it is equal to four times the area in the ﬁrst quadrant. The enclosed area is

0

(2 − 2 ) = 4 2 − 1 3 0 = 4 3 − 1 3 = 4 2 3 = 8 3

3

3

3

3

So = 576 ⇔

8 3

3

= 576 ⇔ 3 = 216 ⇔ =

√

3

216 = 6.

2

= ln 2 −

1

2

≈ 019

rS

Fo

2

1

1

1

− 2 = ln +

1

1

= ln 2 + 1 − (ln 1 + 1)

2

55. =

al

Note that = −6 is another solution, since the graphs are the same.

e

=4

(on [−3 3]) ⇔ sin = 2 sin cos ⇔

ot

57. The curves intersect when tan = 2 sin

N

2 sin cos − sin = 0 ⇔ sin (2 cos − 1) = 0 ⇔ sin = 0 or cos =

3

(2 sin − tan )

[by symmetry]

= 2

1

2

⇔ = 0 or = ± .

3

0

3

= 2 −2 cos − ln |sec |

0

= 2 [(−1 − ln 2) − (−2 − 0)]

= 2(1 − ln 2) = 2 − 2 ln 2

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

225

226

¤

CHAPTER 5

APPLICATIONS OF INTEGRATION

5.2 Volumes

2

1. A cross-section is a disk with radius 2 − 1 so its area is () = 2 − 1 .

2

2

2

() =

1

=

2

1

2

1

2

2 − 1

2

4 − 2 + 1 2

4

2

1

= 4 − 2 + 12 3 1

8

= 8 − 4 + 12 − 4 − 1 +

7

= 1 + 12 = 19

12

1

12

3. A cross-section is a disk with radius

=

5

√

2

√

− 1, so its area is () = − 1 = ( − 1).

() =

5

1

( − 1) =

1

2

5

2 − 1 = 25 − 5 − 1 − 1 = 8

2

2

2

() = 2 .

9

() =

0

9

0

= 4

1

2

2 9

0

2

2 = 4

N

=

, so its area is

ot

5. A cross-section is a disk with radius 2

Fo

rS

1

e

al

=

9

0

= 2(81) = 162

7. A cross-section is a washer (annulus) with inner

radius 3 and outer radius , so its area is

() = ()2 − (3 )2 = (2 − 6 ).

=

1

() =

0

=

0

1

3

3 − 1 7

7

1

0

1

(2 − 6 )

=

1

3

−

1

7

=

4

21

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

SECTION 5.2

VOLUMES

9. A cross-section is a washer with inner radius 2

and outer radius 2, so its area is

() = (2)2 − ( 2 )2 = (4 2 − 4 ).

2

2

() =

(4 2 − 4 )

=

3

−

3

1 5 2

0

5

=

32

3

−

32

5

=

64

15

11. A cross-section is a washer with inner radius 1 −

√ 2

() = (1 − 2 )2 − (1 − )

√

= (1 − 22 + 4 ) − (1 − 2 + )

√

= 4 − 22 + 2 − .

1

√

and outer radius 1 − 2 , so its area is

1

(4 − 22 + 212 − )

1

= 1 5 − 2 3 + 4 32 − 1 2

5

3

3

2

0

=

() =

1

−

5

2

3

+

4

3

0

1

2

−

0

=

11

30

rS

=

al

=

0

4

e

0

13. A cross-section is a washer with inner radius (1 + sec ) − 1 = sec and outer radius 3 − 1 = 2, so its area is

() = 22 − (sec )2 = (4 − sec2 ).

3

() =

−3

= 2

3

−3

3

0

Fo

=

(4 − sec2 )

(4 − sec2 )

[by symmetry]

ot

3

√

= 2 4 − 3 − 0

= 2 4 − tan

3

0

3

√

− 3

N

= 2

4

15. A cross-section is a washer with inner radius 2 − 1 and outer radius 2 −

√

3 , so its area is

√

√

() = (2 − 3 )2 − (2 − 1)2 = 4 − 4 3 + 3 2 − 1 .

=

0

1

() =

0

1

1

(3 − 413 + 23 ) = 3 − 3 43 + 3 23 = 3 − 3 + 3 = 3 .

5

5

5

0

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

¤

227

228

¤

CHAPTER 5

APPLICATIONS OF INTEGRATION

17. From the symmetry of the curves, we see they intersect at =

1

2

and so 2 =

⇔ = ± 1 . A cross-section is a

2

1

2

washer with inner radius 3 − (1 − 2 ) and outer radius 3 − 2 , so its area is

() = (3 − 2 )2 − (2 + 2 )2

= (9 − 62 + 4 ) − (4 + 4 2 + 4 )

= (5 − 10 2 ).

√

12

()

√

−

12

√12

=2

0

5(1 − 22 )

[by symmetry]

√

√22

= 10 22 −

= 10 − 2 3 0

3

= 10

√

2

3

=

10

3

√

2

6

√

2

e

=

1

() =

0

1

()2 =

0

1

3

3

1

0

= 1

3

21. R1 about AB (the line = 1):

1

() =

0

1

0

(1 − )2 =

23. R2 about OA (the line = 0):

1

() =

0

1

0

1

0

1

(1 − 2 + 2 ) = − 2 + 1 3 0 = 1

3

3

1

1

√ 2

12 − 4

(1 − 12 ) = − 2 32 = 1 − 2 = 1

=

3

3

3

0

0

ot

=

Fo

=

rS

=

al

19. R1 about OA (the line = 0):

25. R2 about AB (the line = 1):

1

() =

0

=

1

0

1

0

[12 − (1 − 4 )2 ] =

N

=

(2 4 − 8 ) =

2

5

5 − 1 9

9

1

0

=

2

5

1

0

−

[1 − (1 − 24 + 8 )]

1

9

=

13

45

27. R3 about OA (the line = 0):

=

0

1

() =

0

1

1

1

√

2

4

− 2 =

(12 − 2 ) = 2 32 − 1 3 = 2 − 1 = 1

3

3

3

3

3

0

0

Note: Let R = R1 ∪ R2 ∪ R3 . If we rotate R about any of the segments , , , or , we obtain a right circular cylinder of height 1 and radius 1. Its volume is 2 = (1)2 · 1 = . As a check for Exercises 19, 23, and 27, we can add the answers, and that sum must equal . Thus, 1 + 1 + 1 = .

3

3

3

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

SECTION 5.2

VOLUMES

¤

29. R3 about AB (the line = 1):

=

1

() =

0

=

0

1

0

1

[(1 − 4 )2 − (1 − )2 ] =

( 8 − 2 4 − 2 + 2) =

1

9

9

1

0

[(1 − 2 4 + 8 ) − (1 − 2 + 2 )]

− 2 5 − 1 3 + 2

5

3

1

0

=

1

9

−

Note: See the note in Exercise 27. For Exercises 21, 25, and 29, we have 1 +

3

2

5

−

13

45

1

3

+

+1 =

17

45

17

45

= .

31. (a) About the -axis:

4

0

(tan )2 =

0

tan2

e

≈ 067419

4

(b) About = −1:

4

0

=

=

[tan − (−1)]2 − [0 − (−1)]2

4

0

4

0

[(tan + 1)2 − 12 ]

(tan2 + 2 tan )

33. (a) About = 2:

Fo

≈ 285178

2

−2

2

2

2 − − 1 − 2 4

− 2 − 1 − 2 4

N

⇒ 2 = 1 − 2 4 ⇒

ot

2 + 4 2 = 4 ⇒ 42 = 4 − 2

= ± 1 − 2 4

=

rS

=

al

=

= 2

2

8

0

1 − 2 4 ≈ 78.95684

(b) About = 2:

2 + 4 2 = 4 ⇒ 2 = 4 − 4 2 ⇒ = ± 4 − 4 2

1

2

2

=

2 − − 4 − 4 2

− 2 − 4 − 4 2

−1

= 2

0

1

8 4 − 4 2 ≈ 7895684

[Notice that this is the same approximation as in part (a). This can be explained by Pappus’s Theorem in Section 8.3.]

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

229

¤

230

CHAPTER 5

APPLICATIONS OF INTEGRATION

= 2 + 2 cos and = 4 + + 1 intersect at

35.

= ≈ −1288 and = ≈ 0884

[(2 + 2 cos )2 − (4 + + 1)2 ] ≈ 23780

=

37. =

0

2 sin2 − (−1) − [0 − (−1)]2

39.

0

sin =

al

e

CAS 11 2

= 8

2

√ sin describes the volume of solid obtained by rotating the region

0

rS

√

R = ( ) | 0 ≤ ≤ , 0 ≤ ≤ sin of the -plane about the -axis.

1

( 4 − 8 ) = 0 ( 2 )2 − ( 4 )2 describes the volume of the solid obtained by rotating the region

R = ( ) | 0 ≤ ≤ 1 4 ≤ ≤ 2 of the -plane about the -axis.

1

0

Fo

41.

43. There are 10 subintervals over the 15-cm length, so we’ll use = 102 = 5 for the Midpoint Rule.

=

15

0

() ≈ 5 =

15−0

[(15)

5

+ (45) + (75) + (105) + (135)]

N

ot

= 3(18 + 79 + 106 + 128 + 39) = 3 · 370 = 1110 cm3

10

−

45. (a) = 2 [ ()]2 ≈ 10 4 2 [(3)]2 + [ (5)]2 + [ (7)]2 + [(9)]2

≈ 2 (15)2 + (22)2 + (38)2 + (31)2 ≈ 196 units3

4

(b) = 0 (outer radius)2 − (inner radius)2

≈ 4 − 0 (99)2 − (22)2 + (97)2 − (30)2 + (93)2 − (56)2 + (87)2 − (65)2

4

≈ 838 units3

47. We’ll form a right circular cone with height and base radius by

revolving the line = about the -axis.

2

2

2

2 1 3

=

= 2

=

2

3

0

0

0

1

2 1 3

= 2

= 2

3

3

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

SECTION 5.2

VOLUMES

+ about the -axis.

2

2

2 22

∗

−

− + =

=

+ 2

2

0

0

Another solution: Revolve = −

=

2 3 2 2

− + 2

32

=

0

1

3

2 − 2 + 2 = 1 2

3

and = − to get

0

0

1

1 3

1

− 3 = 2 .

2 − = −

= −

3

3

3

∗

Or use substitution with = −

⇔ 2 = 2 − 2

2

3

3

( − )3

=

= 3 −

− 2 = 2 −

− 2 ( − ) −

3 −

3

3

−

2 3 1

2

= 3 − 3 ( − ) 3 − ( − )2

= 1 23 − ( − ) 32 − 2 − 2 + 2

3

= 1 23 − ( − ) 22 + 2 − 2

3

= 1 23 − 23 − 22 + 2 + 22 + 22 − 3

3

1 2

2

3

2

1

= 3 3 − = 3 (3 − ), or, equivalently, −

3

rS

al

e

49. 2 + 2 = 2

Fo

2

−

=

, so = 1 −

.

2

. So

Similarly, for cross-sections having 2 as their base and replacing , = 2 1 −

1−

=

2 1 −

() =

0

0

2

2

2

=

22 1 −

= 22

1−

+ 2

0

0

2

3

+ 2

= 22 − + 1

= 22 −

3

3 0

N

ot

51. For a cross-section at height , we see from similar triangles that

= 2 2 [ = 1 where is the area of the base, as with any pyramid.]

3

3

53. A cross-section at height is a triangle similar to the base, so we’ll multiply the legs of the base triangle, 3 and 4, by a

proportionality factor of (5 − )5. Thus, the triangle at height has area

5−

5−

1

2

() = · 3

·4

=6 1−

, so

2

5

5

5

5

5

0

= 1 − 5,

2

=

1−

() = 6

= 6

2 (−5 )

5

= − 1

0

0

1

5

1 3 0

1

= −30 3 1 = −30 − 3 = 10 cm3

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

¤

231

232

¤

CHAPTER 5

APPLICATIONS OF INTEGRATION

55. If is a leg of the isosceles right triangle and 2 is the hypotenuse,

then 2 + 2 = (2)2

2

⇒ 2 = 2 2 .

⇒ 22 = 4 2

2

2

() = 2 0 1 ()() = 2 0 2

2

2

2

= 2 0 1 (36 − 92 ) = 9 0 (4 − 2 )

4

2

2

= 9 4 − 1 3 0 = 9 8 − 8 = 24

2

3

2

3

=

−2

() = 2

2

0

57. The cross-section of the base corresponding to the coordinate has length

= 1 − . The corresponding square with side has area

() = 2 = (1 − )2 = 1 − 2 + 2 . Therefore,

1

() =

0

0

1

(1 − 2 + 2 )

1

= − 2 + 1 3 0 = 1 − 1 + 1 − 0 = 1

3

3

3

1

0

1

Or:

(1 − )2 =

2 (−) [ = 1 − ] = 1 3 0 =

3

1

1

3

rS

0

e

al

=

59. The cross-section of the base corresponding to the coordinate has length 1 − 2 . The height also has length 1 − 2 ,

−1

=2·

1

2

0

1

(1 − 22 + 4 )

[by symmetry]

2

3

+

1

5

−0 =

8

15

ot

1

= − 2 3 + 1 5 0 = 1 −

3

5

Fo

so the corresponding isosceles triangle has area () = 1 = 1 (1 − 2 )2 . Therefore,

2

2

1

1

=

(1 − 2 )2

2

61. (a) The torus is obtained by rotating the circle ( − )2 + 2 = 2 about

N

the -axis. Solving for , we see that the right half of the circle is given by

= + 2 − 2 = () and the left half by = − 2 − 2 = ().

So

=

[ ()]2 − [()]2

−

= 2

= 2

2

+ 2 2 − 2 + 2 − 2 − 2 − 2 2 − 2 + 2 − 2

0

0

4

2 − 2 = 8 0 2 − 2

(b) Observe that the integral represents a quarter of the area of a circle with radius , so

8 0 2 − 2 = 8 · 1 2 = 2 2 2 .

4

63. (a) Volume(1 ) =

0

() = Volume(2 ) since the cross-sectional area () at height is the same for both solids.

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

SECTION 5.2

VOLUMES

¤

233

(b) By Cavalieri’s Principle, the volume of the cylinder in the ﬁgure is the same as that of a right circular cylinder with radius and height , that is, 2 .

65. The volume is obtained by rotating the area common to two circles of radius , as

shown. The volume of the right half is

2

2 2 1

2

− 2 +

right = 0 2 = 0

3 2

= 2 − 1 1 +

= 1 3 − 1 3 − 0 −

3 2

2

3

0

So by symmetry, the total volume is twice this, or

1 3

24

3

5

12 .

=

5

3

24

67. Take the -axis to be the axis of the cylindrical hole of radius .

al

A quarter of the cross-section through perpendicular to the

e

Another solution: We observe that the volume is the twice the volume of a cap of a sphere, so we can use the formula from

2

5

Exercise 49 with = 1 : = 2 · 1 2 (3 − ) = 2 1 3 − 1 = 12 3 .

2

3

3

2

2

-axis, is the rectangle shown. Using the Pythagorean Theorem

−

2 − 2 2 − 2 = 8 0 2 − 2 2 − 2

Fo

=

rS

twice, we see that the dimensions of this rectangle are

= 2 − 2 and = 2 − 2 , so

1

2 − 2 2 − 2 , and

4 () = =

() =

−

4

69. (a) The radius of the barrel is the same at each end by symmetry, since the

function = − 2 is even. Since the barrel is obtained by rotating

ot

the graph of the function about the -axis, this radius is equal to the

N

2 value of at = 1 , which is − 1 = − = .

2

2

(b) The barrel is symmetric about the -axis, so its volume is twice the volume of that part of the barrel for 0. Also, the barrel is a volume of rotation, so

2

2 = 2

=2

0

= 2

0

1

2

2

−

1

3

12

+

2

2

2

− 2 = 2 2 − 2 3 + 1 2 5 0

3

5

1 2 5

160

Trying to make this look more like the expression we want, we rewrite it as = 1 22 + 2 − 1 2 +

3

2

2

2

2

2 2

2 2

2

1

3 2 4

1

1 2 4

2 1

2 2

− 40 = ( − ) − 5 4

= − 5 .

But − 2 + 80 = − 4

2

Substituting this back into , we see that = 1 2 + 2 − 2 2 , as required.

3

5

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

3 2 4

80

.

234

¤

CHAPTER 5

APPLICATIONS OF INTEGRATION

5.3 Volumes by Cylindrical Shells

If we were to use the “washer” method, we would ﬁrst have to locate the

1.

local maximum point ( ) of = ( − 1)2 using the methods of

Chapter 3. Then we would have to solve the equation = ( − 1)2 for in terms of to obtain the functions = 1 () and = 2 () shown in the ﬁrst ﬁgure. This step would be difﬁcult because it involves the cubic formula. Finally we would ﬁnd the volume using

= 0 [1 ()]2 − [2 ()]2 .

Using shells, we ﬁnd that a typical approximating shell has radius , so its circumference is 2. Its height is , that is,

1

√

2 3 = 2

0

1

43

0

3 73

7

1

0

= 2

3

7

= 6

7

Fo

= 2

rS

3. =

0

5

1

4

4

3

− 23 + 2 = 2

−2

+

=

5

4

3 0

15

e

0

1

al

( − 1)2 . So the total volume is

1

2 ( − 1)2 = 2

=

2

2(4 − 2 ) = 2 0 (4 − 3 )

2

= 2 22 − 1 4 0 = 2(8 − 4)

4

5. =

2

0

7. 2 = 6 − 22

=

2

0

= 2

N

ot

= 8

⇔ 32 − 6 = 0 ⇔ 3( − 2) = 0 ⇔ = 0 or 2.

2[(6 − 22 ) − 2 ]

2

(−33 + 62 )

0

2

= 2 − 3 4 + 23 0

4

= 2 (−12 + 16) = 8

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

SECTION 5.3

VOLUMES BY CYLINDRICAL SHELLS

1

⇒ = , so

3

1

= 2

1

3

3

= 2 1

= 2

9. = 1

1

= 2(3 − 1) = 4

8

0

= 2

8

( 3 − 0)

43 = 2

0

3 73

7

8

0

6 73

6 7

768

(8 ) =

(2 ) =

7

7

7

Fo

rS

=

e

al

11. = 2

13. The height of the shell is 2 − 1 + ( − 2)2 = 1 − ( − 2)2 = 1 − 2 − 4 + 4 = − 2 + 4 − 3.

= 2

3

1

3

1

(− 2 + 4 − 3)

ot

= 2

(− 3 + 4 2 − 3)

N

3

= 2 − 1 4 + 4 3 − 3 2 1

4

3

2

= 2 − 81 + 36 −

4

8 16

= 2 3 = 3

27

2

− −1 +

4

4

3

−

3

2

15. The shell has radius 2 − , circumference 2(2 − ), and height 4 .

1

2(2 − )4

1

= 2 0 (24 − 5 )

1

= 2 2 5 − 1 6 0

5

6

7

= 2 2 − 1 − 0 = 2 30 =

5

6

=

0

7

15

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

¤

235

236

¤

CHAPTER 5

APPLICATIONS OF INTEGRATION

17. The shell has radius − 1, circumference 2( − 1), and height (4 − 2 ) − 3 = −2 + 4 − 3.

3

2( − 1)(−2 + 4 − 3)

3

= 2 1 (−3 + 52 − 7 + 3)

3

= 2 − 1 4 + 5 3 − 7 2 + 3 1

4

3

2

= 2 − 81 + 45 − 63 + 9 − − 1 +

4

2

4

4 8

= 2 3 = 3

=

1

5

3

−

7

2

+3

19. The shell has radius 1 − , circumference 2(1 − ), and height 1 −

1

2(1 − )(1 − 13 )

1

= 2 0 (1 − − 13 + 43 )

1

= 2 − 1 2 − 3 43 + 3 73

2

4

7

= 3

⇔

=

3

.

0

e

=

3

0

3

2

rS

21. (a) =

al

= 2 1 − 1 − 3 + 3 − 0

2

4

7

5

5

= 2 28 = 14

2 sin

2

−2

= 4

2

−2

( − )[cos4 − (− cos4 )]

( − ) cos4

0

N

(b) ≈ 4650942

25. (a) =

ot

23. (a) = 2

Fo

(b) 9869604

2(4 − )

√ sin

(b) ≈ 3657476

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

SECTION 5.3

27. =

1

0

2

VOLUMES BY CYLINDRICAL SHELLS

¤

√

√

1 + 3 . Let () = 1 + 3 .

Then the Midpoint Rule with = 5 gives

1

0

() ≈

1−0

5

[(01) + (03) + (05) + (07) + (09)]

≈ 02(29290)

Multiplying by 2 gives ≈ 368.

29.

3

0

25 = 2

cylindrical shells.

31.

1

0

3

0

(4 ) . The solid is obtained by rotating the region 0 ≤ ≤ 4 , 0 ≤ ≤ 3 about the y-axis using

2(3 − )(1 − 2 ) . The solid is obtained by rotating the region bounded by (i) = 1 − 2 , = 0, and = 0 or

(ii) = 2 , = 1, and = 0 about the line = 3 using cylindrical shells.

From the graph, the curves intersect at = 0 and at = ≈ 132, with

e

33.

al

+ 2 − 4 0 on the interval (0 ). So the volume of the solid obtained

2

2

0

− sin2 − sin4

ot

CAS 1 3

= 32

rS

Fo

35. = 2

by rotating the region about the -axis is

= 2 0 [( + 2 − 4 )] = 2 0 (2 + 3 − 5 )

= 2 1 3 + 1 4 − 1 6 0 ≈ 405

3

4

6

37. Use shells:

4

2(−2 + 6 − 8) = 2

4

= 2 − 1 4 + 23 − 42 2

4

2

N

=

4

2

(−3 + 62 − 8)

= 2[(−64 + 128 − 64) − (−4 + 16 − 16)]

= 2(4) = 8

√

= ± 2 ± 1

2

(2 − 0)2 −

2 + 1 − 0

39. Use washers: 2 − 2 = 1

=

√

3

√

− 3

= 2

√

3

0

= 2

0

√

3

⇒

[4 − (2 + 1)]

[by symmetry]

√3

(3 − 2 ) = 2 3 − 1 3 0

3

√

√

√

= 2 3 3 − 3 = 4 3

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

237

238

¤

CHAPTER 5

APPLICATIONS OF INTEGRATION

⇔ = ± 1 − ( − 1)2

2

2

2

=

1 − ( − 1)2 =

(2 − 2 )

41. Use disks: 2 + ( − 1)2 = 1

0

0

2

= 2 − 1 3 0 = 4 − 8 = 4

3

3

3

43. + 1 = ( − 1)2

⇔ + 1 = 2 − 2 + 1 ⇔ 0 = 2 − 3

⇔

0 = ( − 3) ⇔ = 0 or 3.

Use disks:

3

=

[( + 1) − (−1)]2 − [( − 1)2 − (−1)]2

0

0

=

3

0

[( + 2)2 − ( 2 − 2 + 2)2 ]

[( 2 + 4 + 4) − ( 4 − 4 3 + 8 2 − 8 + 4)] =

0

(−4 + 4 3 − 7 2 + 12)

117

5

rS

3

= − 1 5 + 4 − 7 3 + 6 2 0 = − 243 + 81 − 63 + 54 =

5

3

5

3

e

3

al

=

45. Use shells:

0

Fo

√

= 2 0 2 2 − 2 = −2 0 (2 − 2 )12 (−2)

= −2 · 2 (2 − 2 )32 = − 4 (0 − 3 ) = 4 3

3

3

3

N

ot

2

−

+

− + = 2

0

0

3

2

2

2

+

=

= 2 −

= 2

3

2 0

6

3

47. = 2

5.4 Work

1. (a) The work done by the gorilla in lifting its weight of 360 pounds to a height of 20 feet

is = = (360 lb)(20 ft) = 7200 ft-lb.

(b) The amount of time it takes the gorilla to climb the tree doesn’t change the amount of work done, so the work done is still 7200 ft-lb.

10

1

10

3. = () = 1 5−2 = 5 −−1

= 5 − 10 + 1 = 45 ft-lb

1

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

SECTION 5.4 WORK

¤

239

5. The force function is given by () (in newtons) and the work (in joules) is the area under the curve, given by

8

0

() =

4

0

() +

8

4

() = 1 (4)(30) + (4)(30) = 180 J.

2

7. According to Hooke’s Law, the force required to maintain a spring stretched units beyond its natural length is proportional

to , that is, () = . Here, the amount stretched is 4 in. =

1

3

ft and the force is 10 lb. Thus, 10 =

= 30 lbft, and () = 30. The work done in stretching the spring from its natural length to 6 in. = length is =

9. (a) If

012

0

12

0

12

30 = 152 0 =

= 2 J, then 2 =

15

4

2 012

2 0

1

1

3

1

2

⇒

ft beyond its natural

ft-lb.

= 1 (00144) = 00072 and =

2

2

00072

=

2500

9

≈ 27778 Nm.

Thus, the work needed to stretch the spring from 35 cm to 40 cm is

110

1

010 2500

1

= 1250 2 120 = 1250 100 − 400 = 25 ≈ 104 J.

9

9

9

24

005

2500

9

and =

270

2500

m = 108 cm

e

(b) () = , so 30 =

02

01

=

2 02

2 01

1

=

4

200

−

1

200

=

3

200 .

=

0

Thus, 2 = 31 .

rS

Now 2 =

01

al

11. The distance from 20 cm to 30 cm is 01 m, so with () = , we get 1 =

2 01

2 0

1

=

1

200 .

In Exercises 13 – 20, is the number of subintervals of length ∆, and ∗ is a sample point in the th subinterval [−1 ].

13. (a) The portion of the rope from ft to ( + ∆) ft below the top of the building weighs

1

2

∆ lb and must be lifted ∗ ft,

Fo

so its contribution to the total work is 1 ∗ ∆ ft-lb. The total work is

2

1 ∗

→∞ =1 2

= lim

∆ =

50

0

1

2

=

1

4

2

50

0

=

2500

4

= 625 ft-lb

Notice that the exact height of the building does not matter (as long as it is more than 50 ft).

N

ot

(b) When half the rope is pulled to the top of the building, the work to lift the top half of the rope is

25

25

1 = 0 1 = 1 2 0 = 625 ft-lb. The bottom half of the rope is lifted 25 ft and the work needed to accomplish

2

4

4

50

50 1 that is 2 = 25 2 · 25 = 25 25 = 625 ft-lb. The total work done in pulling half the rope to the top of the building

2

2 is = 1 + 2 =

625

2

+

625

4

=

3

4

15. The work needed to lift the cable is lim

→∞

· 625 =

=1

1875

4

ft-lb.

2∗ ∆ =

500

0

500

2 = 2 0 = 250,000 ft-lb. The work needed to lift

the coal is 800 lb · 500 ft = 400,000 ft-lb. Thus, the total work required is 250,000 + 400,000 = 650,000 ft-lb.

17. At a height of meters (0 ≤ ≤ 12), the mass of the rope is (08 kgm)(12 − m) = (96 − 08) kg and the mass of the

water is

36

12

kgm (12 − m) = (36 − 3) kg. The mass of the bucket is 10 kg, so the total mass is

(96 − 08) + (36 − 3) + 10 = (556 − 38) kg, and hence, the total force is 98(556 − 38) N. The work needed to lift the bucket ∆ m through the th subinterval of [0 12] is 98(556 − 38∗ )∆, so the total work is

= lim

→∞ =1

98(556 − 38∗ ) ∆ =

12

0

12

(98)(556 − 38) = 98 556 − 192

= 98(3936) ≈ 3857 J

0

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

240

¤

CHAPTER 5

APPLICATIONS OF INTEGRATION

19. A “slice” of water ∆ m thick and lying at a depth of ∗ m (where 0 ≤ ∗ ≤

1

2)

has volume (2 × 1 × ∆) m3 , a mass of

2000 ∆ kg, weighs about (98)(2000 ∆) = 19,600 ∆ N, and thus requires about 19,600∗ ∆ J of work for its removal.

So = lim

→∞ =1

19,600∗ ∆ =

12

0

12

19,600 = 98002 0 = 2450 J.

21. A rectangular “slice” of water ∆ m thick and lying m above the bottom has width m and volume 8 ∆ m3 . It weighs

about (98 × 1000)(8 ∆) N, and must be lifted (5 − ) m by the pump, so the work needed is about

(98 × 103 )(5 − )(8 ∆) J. The total work required is

3

3

3

≈ 0 (98 × 103 )(5 − )8 = (98 × 103 ) 0 (40 − 82 ) = (98 × 103 ) 202 − 8 3 0

3

= (98 × 103 )(180 − 72) = (98 × 103 )(108) = 10584 × 103 ≈ 106 × 106 J

23. Let measure depth (in feet) below the spout at the top of the tank. A horizontal

− ) ft () and volume 2 ∆ = ·

9

(16

64

− )2 ∆ ft3 . It weighs

al

3

(16

8

e

disk-shaped “slice” of water ∆ ft thick and lying at coordinate has radius

about (625) 9 (16 − )2 ∆ lb and must be lifted ft by the pump, so the

64

rS

work needed to pump it out is about (625) 9 (16 − )2 ∆ ft-lb. The total

64

work required is

8

8

≈ 0 (625) 9 (16 − )2 = (625) 9 0 (256 − 32 + 2 )

64

64

= (625) 9 0 (256 − 322 + 3 ) = (625) 9 1282 −

64

64

9 11 264

= 33,000 ≈ 104 × 105 ft-lb

= (625)

64

3

32 3

1 4 8

3 + 4 0

Fo

8

() From similar triangles,

So = 3 + = 3 +

3

= .

8−

8

3

8 (8

− )

=

3

3(8)

+ (8 − )

8

8

=

3

8 (16

− )

25. If only 47 × 105 J of work is done, then only the water above a certain level (call

ot

it ) will be pumped out. So we use the same formula as in Exercise 21, except that

N

the work is ﬁxed, and we are trying to ﬁnd the lower limit of integration:

3

3

47 × 105 ≈ (98 × 103 )(5 − )8 = 98 × 103 202 − 8 3

3

47

⇔

× 102 ≈ 48 = 20 · 32 − 8 · 33 − 202 − 8 3

98

3

3

⇔

23 − 152 + 45 = 0. To ﬁnd the solution of this equation, we plot 23 − 152 + 45 between = 0 and = 3.

We see that the equation is satisﬁed for ≈ 20. So the depth of water remaining in the tank is about 20 m.

27. = 2 , so is a function of and can also be regarded as a function of . If 1 = 2 1 and 2 = 2 2 , then

=

2

() =

1

=

2

2 ( ()) =

1

2

( )

2

( ()) ()

[Let () = 2 , so () = 2 .]

1

by the Substitution Rule.

1

29. (a) =

() =

1 2

−1

1

1

= 1 2

= 1 2

−

2

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

SECTION 5.5

AVERAGE VALUE OF A FUNCTION

¤

1

1

(b) By part (a), =

−

where = mass of the earth in kg, = radius of the earth in m,

+ 1,000,000 and = mass of satellite in kg. (Note that 1000 km = 1,000,000 m.) Thus,

1

1

−11

24

= (667 × 10 )(598 × 10 )(1000) ×

−

≈ 850 × 109 J

637 × 106

737 × 106

5.5 Average Value of a Function

1. ave =

1

−

3. ave =

1

−

5. ave =

1

−

9

() =

1

4−0

() =

1

8−1

() =

1

2−0

4

0

(4 − 2 ) =

1

4

2 1 3 4

2 − 3 0 = 1 32 −

4

8

8 √

3

= 1 3 43 =

7 4

1

3

(16

28

1

2

0

2 (1 + 3 )4 =

9

1

2

1

1

4

3

− 1) =

45

28

64

3

− 0 = 1 32 =

4 3

8

3

[ = 1 + 3 , = 32 ]

5

1

=

1

(95

30

− 1) =

al

5

e

29,524

= 196826

15

−1

1

1

= − 0 0 cos4 sin = 1 4 (−) [ = cos , = − sin ]

1

1

1

1

1

2

2

= −1 4 = · 2 0 4 [by Theorem 4.5.6(a)] = 1 5 0 = 5

5

1

6

7. ave

1

rS

5

5

1

1 1

( − 3)2 =

( − 3)3

5−2 2

3 3

2

3

1

= 1 2 − (−1)3 = 9 (8 + 1) = 1

9

(c)

Fo

9. (a) ave =

(b) () = ave

⇔ ( − 3)2 = 1 ⇔

− 3 = ±1 ⇔ = 2 or 4

ot

1

(2 sin − sin 2)

−0 0

1

= −2 cos + 1 cos 2 0

2

1

4

= 2 + 1 − −2 + 1 =

2

2

(c)

N

11. (a) ave =

(b) () = ave

⇔ 2 sin − sin 2 =

4

1 ≈ 1238 or 2 ≈ 2808

⇔

13. is continuous on [1 3], so by the Mean Value Theorem for Integrals there exists a number in [1 3] such that

3

1

() = ()(3 − 1) ⇒ 8 = 2 (); that is, there is a number such that () =

8

2

= 4.

15. Use geometric interpretations to ﬁnd the values of the integrals.

8

0

() =

=

1

0

() +

−1

2

+

1

2

+

1

2

2

1

() +

+1+4+

3

2

3

2

() +

+2=9

Thus, the average value of on [0 8] = ave =

1

8−0

8

0

4

3

() +

6

4

() +

7

6

() +

8

7

()

() = 1 (9) = 9 .

8

8

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

241

242

¤

CHAPTER 5 APPLICATIONS OF INTEGRATION

17. Let = 0 and = 12 correspond to 9 AM and 9 PM , respectively.

12

12

1

1

1

50 + 14 sin 12 = 12 50 − 14 · 12 cos 12 0

0

1

= 12 50 · 12 + 14 · 12 + 14 · 12 = 50 + 28 ◦ F ≈ 59 ◦ F

1

12 − 0

ave =

19. ave

1

=

8

21. ave =

=

0

1 5

5

0

1

4

8

12

3

√

=

2

+1

() =

−

23. Let () =

5

2

1

5

5

5

0 4

0

8

√

8

( + 1)−12 = 3 + 1 0 = 9 − 3 = 6 kgm

1 − cos 2 =

5

5

sin 2 0 =

5

1

4

[(5 − 0) − 0] =

1

4

5

4

5

1 − cos 2

5

0

≈ 04 L

() for in [ ]. Then is continuous on [ ] and differentiable on ( ), so by the Mean Value

e

Theorem there is a number in ( ) such that () − () = 0 ()( − ). But 0 () = () by the Fundamental

Theorem of Calculus. Therefore, () − 0 = ()( − ).

rS

al

5 Review

1. (a) See Section 5.1, Figure 2 and Equations 5.1.1 and 5.1.2.

(b) Instead of using “top minus bottom” and integrating from left to right, we use “right minus left” and integrate from bottom

Fo

to top. See Figures 11 and 12 in Section 5.1.

2. The numerical value of the area represents the number of meters by which Sue is ahead of Kathy after 1 minute.

3. (a) See the discussion in Section 5.2, near Figures 2 and 3, ending in the Deﬁnition of Volume.

(b) See the discussion between Examples 5 and 6 in Section 5.2. If the cross-section is a disk, ﬁnd the radius in terms of or

ot

and use = (radius)2 . If the cross-section is a washer, ﬁnd the inner radius in and outer radius out and use

2

2

= out − in .

N

4. (a) = 2 ∆ = (circumference)(height)(thickness)

(b) For a typical shell, ﬁnd the circumference and height in terms of or and calculate

= (circumference)(height)( or ), where and are the limits on or .

(c) Sometimes slicing produces washers or disks whose radii are difﬁcult (or impossible) to ﬁnd explicitly. On other occasions, the cylindrical shell method leads to an easier integral than slicing does.

5.

6

0

() represents the amount of work done. Its units are newton-meters, or joules.

6. (a) The average value of a function on an interval [ ] is ave =

1

−

() .

(b) The Mean Value Theorem for Integrals says that there is a number at which the value of is exactly equal to the average value of the function, that is, () = ave . For a geometric interpretation of the Mean Value Theorem for Integrals, see

Figure 2 in Section 5.5 and the discussion that accompanies it. c ° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

CHAPTER 5 REVIEW

1. The curves intersect when 2 = 4 − 2

¤

243

⇔ 22 − 4 = 0 ⇔

2( − 2) = 0 ⇔ = 0 or 2.

2

2

= 0 (4 − 2 ) − 2 = 0 (4 − 22 )

2

= 22 − 2 3 0 = 8 −

3

16

3

−0 =

8

3

3. If ≥ 0, then | | = , and the graphs intersect when = 1 − 22

12

12

(1 − 22 ) − = 2 0 (−22 − + 1)

0

12

1

= 2 − 2 3 − 1 2 + 0 = 2 − 12 −

3

2

7

7

= 2 24 = 12

sin

− (2 − 2)

2

0

2

1

2

= − cos

− 3 + 2

2

3

0

2

2

8

= − 3 + 4 − − − 0 + 0 =

2

+

1

2

−0

Fo

5. =

1

8

al

= 2

e

or −1, but −1 0. By symmetry, we can double the area from = 0 to = 1 .

2

1

2

rS

=

⇔ 22 + − 1 = 0 ⇔ (2 − 1)( + 1) = 0 ⇔

4

3

+

4

ot

7. Using washers with inner radius 2 and outer radius 2, we have

2

2

(2)2 − (2 )2 = 0 (42 − 4 )

0

2

= 4 3 − 1 5 0 = 32 − 32

3

5

3

5

N

=

= 32 ·

9. =

2

15

=

64

15

3

2

(9 − 2 ) − (−1) − [0 − (−1)]2

−3

= 2

3

3

(10 − 2 )2 − 1 = 2 0 (100 − 20 2 + 4 − 1)

0

3

(99 − 20 2 + 4 ) = 2 99 −

= 2 297 − 180 + 243 = 1656

5

5

= 2

0

20 3

3

+ 1 5

5

3

0

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

244

¤

CHAPTER 5 APPLICATIONS OF INTEGRATION

11. The graph of 2 − 2 = 2 is a hyperbola with right and left branches.

√

⇒ = ± 2 − 2 .

Solving for gives us 2 = 2 − 2

We’ll use shells and the height of each shell is

√

√

√

2 − 2 − − 2 − 2 = 2 2 − 2 .

√

+

2 · 2 2 − 2 . To evaluate, let = 2 − 2 ,

The volume is =

so = 2 and =

1

2

. When = , = 0, and when = + ,

= ( + )2 − 2 = 2 + 2 + 2 − 2 = 2 + 2 .

13. A shell has radius

2

− , circumference 2

= cos2 intersects =

±1

2

cos =

=

when cos2 =

[ || ≤ 2] ⇔ =

3

2

−3

1

4

2

1

4

− , and height cos2 − 1 .

4

⇔

e

0

2+2

√ 1

32

2 32

4

= 2

= 2 + 2

.

2

3

3

0

±.

3

1

− cos2 −

2

4

al

2+2

rS

Thus, = 4

15. (a) A cross-section is a washer with inner radius 2 and outer radius .

=

1 2

1

1

() − (2 )2 = 0 (2 − 4 ) = 1 3 − 1 5 0 = 1 − 1 =

3

5

3

5

0

Fo

(b) A cross-section is a washer with inner radius and outer radius .

1

1

1 2

2

= 0

− = 0 ( − 2 ) = 1 2 − 1 3 0 = 1 − 1 =

2

3

2

3

2

15

6

ot

(c) A cross-section is a washer with inner radius 2 − and outer radius 2 − 2 .

1

1

1

= 0 (2 − 2 )2 − (2 − )2 = 0 (4 − 52 + 4) = 1 5 − 5 3 + 22 0 = 1 −

5

3

5

17. (a) Using the Midpoint Rule on [0 1] with () = tan(2 ) and = 4, we estimate

5

3

+2 =

8

15

2

2

2

2 tan 1

+ tan 3

+ tan 5

+ tan 7

≈ 1 (153) ≈ 038

8

8

8

8

4

N

=

1

0

tan(2 ) ≈

1

4

(b) Using the Midpoint Rule on [0 1] with () = tan2 (2 ) (for disks) and = 4, we estimate

=

19.

21.

2

0

1

0

2

2

2

2

+ tan2 3

+ tan2 5

+ tan2 7

≈

() ≈ 1 tan2 1

4

8

8

8

8

2 cos =

2

0

0

(2 − sin )2

≈ 087

(2) cos

The solid is obtained by rotating the region R = ( ) | 0 ≤ ≤

4 (1114)

20

≤ ≤ cos about the -axis.

The solid is obtained by rotating the region R = {( ) | 0 ≤ ≤ 0 ≤ ≤ 2 − sin } about the -axis.

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

CHAPTER 5 REVIEW

23. Take the base to be the disk 2 + 2 ≤ 9. Then =

3

−3

() , where (0 ) is the area of the isosceles right triangle

whose hypotenuse lies along the line = 0 in the -plane. The length of the hypotenuse is 2 each leg is

√ √

√ √

2

2 9 − 2 . () = 1 2 9 − 2 = 9 − 2 , so

2

=2

3

0

() = 2

3

0

· 1 ·

4

27. () =

=

008

0

√

3

8

=

√

3 2

64 .

=

20

0

() =

√

3

64

20

0

2 =

√

3

64

√

3

.

8

1

3 20

3 0

Therefore,

=

√

8000 3

64 · 3

=

√

125 3

3

m3 .

⇒ 30 N = (15 − 12) cm ⇒ = 10 Ncm = 1000 Nm. 20 cm − 12 cm = 008 m ⇒

= 1000

008

0

008

= 500 2 0 = 500(008)2 = 32 N·m = 32 J.

e

1

2

√

9 − 2 and the length of

3

(9 − 2 ) = 2 9 − 1 3 0 = 2(27 − 9) = 36

3

25. Equilateral triangles with sides measuring 1 meters have height 1 sin 60◦ =

4

4

() =

¤

29. (a) The parabola has equation = 2 with vertex at the origin and passing through

1

4

⇒ = 1 2

4

⇒ 2 = 4

⇒

. Each circular disk has radius 2 and is moved 4 − ft.

4 2

4

= 0 2 625(4 − ) = 250 0 (4 − )

rS

=2

⇒ =

al

(4 4). 4 = · 42

64

3

=

8000

3

≈ 8378 ft-lb

Fo

4

= 250 2 2 − 1 3 0 = 250 32 −

3

(b) In part (a) we knew the ﬁnal water level (0) but not the amount of work done. Here we use the same equation, except with the work ﬁxed, and the lower limit of

ot

integration (that is, the ﬁnal water level — call it ) unknown: = 4000 ⇔

4

250 22 − 1 3 = 4000 ⇔ 16 = 32 − 64 − 22 − 1 3

⇔

3

3

3

3 − 62 + 32 −

48

= 0. We graph the function () = 3 − 62 + 32 −

48

N

on the interval [0 4] to see where it is 0. From the graph, () = 0 for ≈ 21.

So the depth of water remaining is about 21 ft.

31. lim ave = lim

→0

→0

1

( + ) −

+

() = lim

→0

( + ) − ()

, where () = () . But we recognize this

limit as being 0 () by the deﬁnition of a derivative. Therefore, lim ave = 0 () = () by FTC1.

→0

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

245

N ot e

al

rS

Fo

PROBLEMS PLUS

1. (a) The area under the graph of from 0 to is equal to

() , so the requirement is that

0

0

() = 3 for all . We

differentiate both sides of this equation with respect to (with the help of FTC1) to get () = 32 . This function is positive and continuous, as required.

(b) The volume generated from = 0 to = is

0

[ ()]2 . Hence, we are given that 2 =

0

[ ()]2 for all

0. Differentiating both sides of this equation with respect to using the Fundamental Theorem of Calculus gives

2 = [()]2 ⇒ () = 2, since is positive. Therefore, () = 2.

3. Let and be the -coordinates of the points where the line intersects the

curve. From the ﬁgure, 1 = 2

e

⇒

− 42 +

27 4

4

= 42 −

= 42 −

27 4

4

27 4

4

−

rS

27 4

0

4

− 42 +

al

− 8 − 273 = 8 − 273 −

0

− − 42 −

27 4

4

− = 42 −

= 42 −

27 4

4

− 82 + 274 =

= 2

16

81

81

4

−

− 8 − 273

81 4

4

− 42

2 − 4

64

⇒ = 4 . Thus, = 8 − 273 = 8 4 − 27 729 =

9

9

32

9

−

64

27

=

32

.

27

ot

So for 0, 2 =

27 4

4

Fo

0 = 42 −

27 4

4

5. (a) = 2 ( − 3) =

1

2 (3

3

− ). See the solution to Exercise 5.2.49.

N

(b) The smaller segment has height = 1 − and so by part (a) its volume is

= 1 (1 − )2 [3(1) − (1 − )] = 1 ( − 1)2 ( + 2). This volume must be 1 of the total volume of the sphere,

3

3

3

4 which is 4 (1)3 . So 1 ( − 1)2 ( + 2) = 1 3 ⇒ (2 − 2 + 1)( + 2) = 4 ⇒ 3 − 3 + 2 = 4 ⇒

3

3

3

3

3

33 − 9 + 2 = 0. Using Newton’s method with () = 33 − 9 + 2, 0 () = 92 − 9, we get

+1 = −

33 − 9 + 2

. Taking 1 = 0, we get 2 ≈ 02222, and 3 ≈ 02261 ≈ 4 , so, correct to four decimal

92 − 9

places, ≈ 02261.

(c) With = 05 and = 075, the equation 3 − 32 + 43 = 0 becomes 3 − 3(05)2 + 4(05)3 (075) = 0 ⇒

3 − 3 2 + 4 1 3 = 0 ⇒ 83 − 122 + 3 = 0. We use Newton’s method with () = 83 − 122 + 3,

2

8 4

0 () = 242 − 24, so +1 = −

83 − 122 + 3

. Take 1 = 05. Then 2 ≈ 06667, and 3 ≈ 06736 ≈ 4 .

242 − 24

So to four decimal places the depth is 06736 m.

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

247

248

¤

CHAPTER 5 PROBLEMS PLUS

(d) (i) From part (a) with = 5 in., the volume of water in the bowl is

= 1 2 (3 − ) = 1 2 (15 − ) = 52 − 1 3 . We are given that

3

3

3

when = 3. Now

= 02 in3s and we want to ﬁnd

02

= 10

− 2 , so

=

. When = 3, we have

(10 − 2 )

02

1

=

=

≈ 0003 ins.

(10 · 3 − 32 )

105

(ii) From part (a), the volume of water required to ﬁll the bowl from the instant that the water is 4 in. deep is

=

1

2

· 4 (5)3 − 1 (4)2 (15 − 4) =

3

3

743

02

this volume by the rate: Time =

2

3

· 125 −

=

370

3

16

3

· 11 =

74

3 .

To ﬁnd the time required to ﬁll the bowl we divide

≈ 387 s ≈ 65 min.

7. We are given that the rate of change of the volume of water is

= −(), where is some positive constant and () is

. But by the Chain Rule,

=

, so the ﬁrst equation can be written

al

with respect to time, that is,

e

the area of the surface when the water has depth . Now we are concerned with the rate of change of the depth of the water

rS

= −() (). Also, we know that the total volume of water up to a depth is () = 0 () , where () is

the area of a cross-section of the water at a depth . Differentiating this equation with respect to , we get = ().

Substituting this into equation , we get ()() = −() ⇒ = −, a constant.

9. We must ﬁnd expressions for the areas and , and then set them equal and see what this says about the curve . If

Fo

= 22 , then area is just 0 (22 − 2 ) = 0 2 = 1 3 . To ﬁnd area , we use as the variable of

3

integration. So we ﬁnd the equation of the middle curve as a function of : = 22 ⇔ = 2, since we are

concerned with the ﬁrst quadrant only. We can express area as

0

22

22 22

22

4

4

(2)32

2 − () =

−

() = 3 −

()

3

3

0

0

0

ot

N

where () is the function with graph . Setting = , we get 1 3 = 4 3 −

3

3

22

0

()

⇔

22

0

() = 3 .

Now we differentiate this equation with respect to using the Chain Rule and the Fundamental Theorem:

(22 )(4) = 32 ⇒ () = 3 2, where = 22 . Now we can solve for : = 3 2 ⇒

4

4

2 =

9

16 (2)

⇒ =

32 2

9 .

11. (a) Stacking disks along the -axis gives us =

(b) Using the Chain Rule,

0

[ ()]2 .

=

·

= [ ()]2

.

√

√

14

√

. Set

= : [ ()]2 = ⇒ [ ()]2 =

; that

= [ ()]2

⇒ () =

14

. The advantage of having

= is that the markings on the container are equally spaced. is, () =

(c)

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

CHAPTER 5 PROBLEMS PLUS

13. The cubic polynomial passes through the origin, so let its equation be

= 3 + 2 + . The curves intersect when 3 + 2 + = 2

⇔

3 + ( − 1)2 + = 0. Call the left side (). Since () = () = 0 another form of is

() = ( − )( − ) = [2 − ( + ) + ]

= [3 − ( + )2 + ]

Since the two areas are equal, we must have

0

() = −

() ⇒

e

[ ()] = [ ()] ⇒ () − (0) = () − () ⇒ (0) = (), where is an antiderivative of .

0

Now () = () = [3 − ( + )2 + ] = 1 4 − 1 ( + )3 + 1 2 + , so

4

3

2

(0) = () ⇒ = 1 4 − 1 ( + )3 + 1 3 + ⇒ 0 = 1 4 − 1 ( + )3 + 1 3 ⇒

4

3

2

4

3

2

0 = 3 − 4( + ) + 6 [multiply by 12(3 ), 6= 0] ⇒ 0 = 3 − 4 − 4 + 6 ⇒ = 2.

N

ot

Fo

rS

al

Hence, is twice the value of .

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

¤

249

N ot e

al

rS

Fo

6

INVERSE FUNCTIONS:

Exponential, Logarithmic, and Inverse Trigonometric Functions

6.1 Inverse Functions

1. (a) See Deﬁnition 1.

(b) It must pass the Horizontal Line Test.

3. is not one-to-one because 2 6= 6, but (2) = 20 = (6).

5. We could draw a horizontal line that intersects the graph in more than one point. Thus, by the Horizontal Line Test, the

function is not one-to-one.

e

7. No horizontal line intersects the graph more than once. Thus, by the Horizontal Line Test, the function is one-to-one.

−2

=−

= 1. Pick any -values equidistant

2

2(1)

al

9. The graph of () = 2 − 2 is a parabola with axis of symmetry = −

from 1 to ﬁnd two equal function values. For example, (0) = 0 and (2) = 0, so is not one-to-one.

1 6= 2

⇒ 11 6= 12

⇒ (1 ) 6= (2 ), so is one-to-one.

rS

11. () = 1.

Geometric solution: The graph of is the hyperbola shown in Figure 14 in Section 1.2. It passes the Horizontal Line Test, so is one-to-one.

Fo

13. () = 1 + cos is not one-to-one since ( + 2) = () for any real number and any integer .

15. A football will attain every height up to its maximum height twice: once on the way up, and again on the way down.

Thus, even if 1 does not equal 2 , (1 ) may equal (2 ), so is not 1-1.

⇔ −1 (17) = 6.

ot

17. (a) Since is 1-1, (6) = 17

(b) Since is 1-1, −1 (3) = 2 ⇔ (2) = 3.

√

√

⇒ 0 () = 1 + 1(2 ) 0 on (0 ∞). So is increasing and hence, 1-1. By inspection,

√

(4) = 4 + 4 = 6, so −1 (6) = 4.

N

19. () = +

21. We solve =

5

(

9

− 32) for : 9 = − 32 ⇒ = 9 + 32. This gives us a formula for the inverse function, that

5

5

is, the Fahrenheit temperature as a function of the Celsius temperature . ≥ −45967 ⇒

9

5

9

5

+ 32 ≥ −45967 ⇒

≥ −49167 ⇒ ≥ −27315, the domain of the inverse function.

23. = () = 3 − 2

25. = () = 1 +

⇒ 2 = 3 −

√

2 + 3

( ≥ 1)

⇒ =

3−

3−

3−

. Interchange and : =

. So −1 () =

.

2

2

2

⇒ −1=

√

2 + 3

⇒ ( − 1)2 = 2 + 3 ⇒ ( − 1)2 − 2 = 3 ⇒

= 1 ( − 1)2 − 2 . Interchange and : = 1 ( − 1)2 − 2 . So −1 () = 1 ( − 1)2 − 2 . Note that the domain of −1

3

3

3

3

3

3 is ≥ 1.

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

251

252

¤

CHAPTER 6

INVERSE FUNCTIONS

√

1−

√ , the domain is ≥ 0. (0) = 1 and as increases, decreases. As → ∞,

27. For () =

1+

√

√

√

1 − 1

1 − 1

−1

√ · √ = √

= −1, so the range of is −1 ≤ 1. Thus, the domain of −1 is −1 ≤ 1.

→

1

1 + 1

1 + 1

√

√

√

√

√

√

√

1−

√

=

+ = 1− ⇒

⇒ (1 + ) = 1 − ⇒ + = 1 − ⇒

1+

2

2

√

√

1−

1−

1−

(1 + ) = 1 − ⇒

=

. Interchange and : =

. So

⇒ =

1+

1+

1+

2

1− with −1 ≤ 1.

−1 () =

1+

√

⇒ − 1 = 4 ⇒ = 4 − 1 [not ± since

√

√

≥ 0]. Interchange and : = 4 − 1. So −1 () = 4 − 1. The

√

√ graph of = 4 − 1 is just the graph of = 4 shifted right one unit.

rS

al

From the graph, we see that and −1 are reﬂections about the line = .

e

29. = () = 4 + 1

31. Reﬂect the graph of about the line = . The points (−1 −2), (1 −1),

(2 2), and (3 3) on are reﬂected to (−2 −1), (−1 1), (2 2), and (3 3)

33. (a) = () =

2

2

Fo

on −1 .

√

1 − 2

(0 ≤ ≤ 1 and note that ≥ 0) ⇒

⇒ = 1 − 2 ⇒ = 1 − 2 . So

2

ot

=1−

√

−1 () = 1 − 2 , 0 ≤ ≤ 1. We see that −1 and are the same function. N

(b) The graph of is the portion of the circle 2 + 2 = 1 with 0 ≤ ≤ 1 and

0 ≤ ≤ 1 (quarter-circle in the ﬁrst quadrant). The graph of is symmetric with respect to the line = , so its reﬂection about = is itself, that is,

−1 = .

35. (a) 1 6= 2

⇒ 3 6= 3

1

2

⇒ (1 ) 6= (2 ), so is one-to-one.

(b) () = 3 and (2) = 8 ⇒ −1 (8) = 2, so ( −1 )0 (8) = 1 0 ( −1 (8)) = 1 0 (2) =

0

2

(c) = 3

⇒ = 13 . Interchanging and gives = 13 ,

so −1 () = 13 . Domain −1 = range() = R.

1

.

12

(e)

Range( −1 ) = domain( ) = R.

(d) −1 () = 13 ⇒ ( −1 )0 () = 1 −23

3

−1 0

1 1

1

( ) (8) = 3 4 = 12 as in part (b).

⇒

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

SECTION 6.1

37. (a) Since ≥ 0, 1 6= 2

⇒ 2 6= 2

1

2

⇒ 9 − 2 6= 9 − 2

1

2

(b) 0 () = −2 and (1) = 8 ⇒ −1 (8) = 1, so ( −1 )0 (8) =

√

⇒ 2 = 9 − ⇒ = 9 − .

√

√

Interchange and : = 9 − , so −1 () = 9 − .

INVERSE FUNCTIONS

¤

253

⇒ (1 ) 6= (2 ), so is 1-1.

1

1

1

1

= 0

=

=− .

0 ( −1 (8))

(1)

−2

2

(c) = 9 − 2

(e)

Domain( −1 ) = range ( ) = [0 9].

Range( −1 ) = domain ( ) = [0 3].

√

(d) ( −1 )0 () = −1 2 9 −

⇒ ( −1 )0 (8) = − 1 as in part (b).

2

⇒ −1 (4) = 0, and () = 23 + 32 + 7 + 4 ⇒ 0 () = 62 + 6 + 7 and 0 (0) = 7.

0 (0) =

2

43. (4) = 5

(3) =

⇒ −1 (5) = 4. Thus, ( −1 )0 (5) =

2

sec2 (2) and

1

1

1

3

= 0

=

= .

0 ( −1 (5))

(4)

23

2

√

√

1 + 3 ⇒ 0 () = 1 + 3 0, so is an increasing function and it has an inverse. Since

3

3√

1 + 3 = 0, −1 (0) = 3. Thus, ( −1 )0 (0) =

3

Fo

45. () =

⇒ −1 (3) = 0, and () = 3 + 2 + tan(2) ⇒ 0 () = 2 +

0

· 1 = . Thus, −1 (3) = 1 0 −1 (3) = 1 0 (0) = 2.

2

rS

41. (0) = 3

1

1

1

= 0

= .

0 ( −1 (4))

(0)

7

e

Thus, ( −1 )0 (4) =

al

39. (0) = 4

1

1

1

1

= √ .

= 0

= √

3

0 ( −1 (0))

(3)

1+3

28

√

3 + 2 + + 1 is increasing, so is 1-1.

(We could verify this by showing that 0 () 0.) Enter = 3 + 2 + + 1

47. We see that the graph of = () =

ot

and use your CAS to solve the equation for . Using Derive, we get two

(irrelevant) solutions involving imaginary expressions, as well as one which can be

N

simpliﬁed to the following:

√ √

√

√

3

= −1 () = − 64 3 − 272 + 20 − 3 + 272 − 20 + 3 2

√ √ where = 3 3 274 − 402 + 16.

Maple and Mathematica each give two complex expressions and one real expression, and the real expression is equivalent

to that given by Derive. For example, Maple’s expression simpliﬁes to

= 1082 + 12

1 23 − 8 − 2 13

, where

6

2 13

√

48 − 1202 + 814 − 80.

49. (a) If the point ( ) is on the graph of = (), then the point ( − ) is that point shifted units to the left. Since

is 1-1, the point ( ) is on the graph of = −1 () and the point corresponding to ( − ) on the graph of is

( − ) on the graph of −1 . Thus, the curve’s reﬂection is shifted down the same number of units as the curve itself is shifted to the left. So an expression for the inverse function is −1 () = −1 () − . c ° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

254

¤

CHAPTER 6 INVERSE FUNCTIONS

(b) If we compress (or stretch) a curve horizontally, the curve’s reﬂection in the line = is compressed (or stretched) vertically by the same factor. Using this geometric principle, we see that the inverse of () = () can be expressed as

−1 () = (1) −1 ().

6.2 Exponential Functions and Their Derivatives

1. (a) () = , 0

(b) R

(c) (0 ∞)

(d) See Figures 6(c), 6(b), and 6(a), respectively.

3. All of these graphs approach 0 as → −∞, all of them pass through the point

(0 1), and all of them are increasing and approach ∞ as → ∞. The larger the base, the faster the function increases for 0, and the faster it approaches 0 as

with bases less than 1

1

3

and

1

10

are decreasing. The graph of

1

10

1

3

is the

is the reﬂection of

rS

reﬂection of that of 3 about the -axis, and the graph of

al

5. The functions with bases greater than 1 (3 and 10 ) are increasing, while those

e

→ −∞.

that of 10 about the -axis. The graph of 10 increases more quickly than that of

7. We start with the graph of = 10

Fo

3 for 0, and approaches 0 faster as → −∞.

(Figure 3) and shift it 2 units to the left to

N

ot

obtain the graph of = 10+2 .

9. We start with the graph of = 2 (Figure 2),

reﬂect it about the -axis, and then about the

-axis (or just rotate 180◦ to handle both reﬂections) to obtain the graph of = −2− .

In each graph, = 0 is the horizontal asymptote. = 2

= 2−

= −2−

11. We start with the graph of = (Figure 12) and reﬂect about the -axis to get the graph of = − . Then we compress

the graph vertically by a factor of 2 to obtain the graph of = 1 − and then reﬂect about the -axis to get the graph of

2

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

SECTION 6.2 EXPONENTIAL FUNCTIONS AND THEIR DERIVATIVES

¤

255

= − 1 − . Finally, we shift the graph upward one unit to get the graph of = 1 − 1 − .

2

2

13. (a) To ﬁnd the equation of the graph that results from shifting the graph of = 2 units downward, we subtract 2 from the

original function to get = − 2.

(b) To ﬁnd the equation of the graph that results from shifting the graph of = 2 units to the right, we replace with − 2 in the original function to get = (−2) .

e

(c) To ﬁnd the equation of the graph that results from reﬂecting the graph of = about the -axis, we multiply the original

al

function by −1 to get = − . the original function to get = − .

rS

(d) To ﬁnd the equation of the graph that results from reﬂecting the graph of = about the -axis, we replace with − in

(e) To ﬁnd the equation of the graph that results from reﬂecting the graph of = about the -axis and then about the

get = −− .

Fo

-axis, we ﬁrst multiply the original function by −1 (to get = − ) and then replace with − in this equation to

2

15. (a) The denominator is zero when 1 − 1− = 0

⇔

2

2

1− = 1

⇔

1 − 2 = 0

⇔

= ±1. Thus,

1− has domain { | 6= ±1} = (−∞ −1) ∪ (−1 1) ∪ (1 ∞).

1 − 1−2

1+

(b) The denominator is never equal to zero, so the function () = cos has domain R, or (−∞ ∞).

6 3

6

= and 24 = 3 ⇒ 24 =

17. Use = with the points (1 6) and (3 24). 6 = 1

N

ot

the function () =

4 = 2

⇒ = 2 [since 0] and =

19. 2 ft = 24 in, (24) = 242 in = 576 in = 48 ft.

6

2

= 3. The function is () = 3 · 2 .

(24) = 224 in = 224 (12 · 5280) mi ≈ 265 mi

21. The graph of ﬁnally surpasses that of at ≈ 358.

23. lim (1001) = ∞ by (3), since 1001 1.

→∞

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

⇒

256

¤

CHAPTER 6 INVERSE FUNCTIONS

25. Divide numerator and denominator by 3 : lim

→∞

3 − −3

1 − −6

1−0

=1

= lim

=

3 + −3

→∞ 1 + −6

1+0

27. Let = 3(2 − ). As → 2+ , → −∞. So lim 3(2−) = lim = 0 by (10).

→−∞

→2+

29. Since −1 ≤ cos ≤ 1 and −2 0, we have −−2 ≤ −2 cos ≤ −2 . We know that lim (−−2 ) = 0 and

→∞

lim −2 = 0, so by the Squeeze Theorem, lim (−2 cos ) = 0.

→∞

→∞

31. () = 5 is a constant function, so its derivative is 0, that is, 0 () = 0.

33. By the Product Rule, () = (3 + 2)

⇒

0 () = (3 + 2)( )0 + (3 + 2)0 = (3 + 2) + (32 + 2)

39. () =

0

1

⇒ () =

√

1 + 23

−1

1

1 −1

=

1

=

2

2

⇒ 0 () = sin 2 ( sin 2)0 = sin 2 ( · 2 cos 2 + sin 2 · 1) = sin 2 (2 cos 2 + sin 2)

⇒ 0 =

⇒ 0 = ·

1

1

33

(23 · 3) = √

(1 + 23 )−12

(1 + 23 ) = √

3

2

2 1 + 2

1 + 23

( ) = · or +

+

+

⇒

N

47. By the Quotient Rule, =

0 =

·

ot

45. =

3

(3 ) = 32 .

⇒ 0 = − (−) + − · 1 = − (− + 1) or (1 − )−

41. By (9), () = sin 2

43. =

3

rS

1

⇒ 0 =

Fo

37. = −

3

al

35. By (9), =

e

= [(3 + 2) + (32 + 2)] = (3 + 32 + 2 + 2)

( + )( ) − ( + )( )

( + − − )

( − )

=

=

.

( + )2

( + )2

( + )2

49. = cos

1 − 2

1 + 2

⇒

1 − 2

1 − 2

1 − 2

(1 + 2 )(−22 ) − (1 − 2 )(22 )

= − sin

·

= − sin

·

2

2

2

1+

1 +

1+

(1 + 2 )2

−22 (1 + 2 ) + (1 − 2 )

−22 (2)

1 − 2

1 − 2

42

1 − 2

·

·

= − sin

= − sin

=

· sin

1 + 2

(1 + 2 )2

1 + 2

(1 + 2 )2

(1 + 2 )2

1 + 2

0

51. = 2 cos

⇒ 0 = 2 (− sin ) + (cos )(22 ) = 2 (2 cos − sin ).

At (0 1), 0 = 1(2 − 0) = 2, so an equation of the tangent line is − 1 = 2( − 0), or = 2 + 1. c ° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

SECTION 6.2 EXPONENTIAL FUNCTIONS AND THEIR DERIVATIVES

53.

( ) =

( − ) ⇒

·

· 1 − · 0

= 1 − 0

2

·

= 1 − 0

⇒

·

¤

257

⇒

0

1

−

· = 1 − 0

2

0 −

⇒

0

· =1−

2

⇒

−

( − )

⇒ 0 = 2

= 2

−

−

2

−

0 1 −

=

2

55. = + −2

⇒ 0 = − 1 −2 ⇒ 00 = + 1 −2 , so

2

4

200 − 0 − = 2 + 1 −2 − − 1 −2 − + −2 = 0.

4

2

57. =

⇒ 0 =

⇒

00 = 2 , so if = satisﬁes the differential equation 00 + 6 0 + 8 = 0,

e

then 2 + 6 + 8 = 0; that is, (2 + 6 + 8) = 0. Since 0 for all , we must have 2 + 6 + 8 = 0,

000 () = 22 · 22 = 23 2

⇒ 00 () = 2 · 22 = 22 2

⇒ ···

⇒

⇒ () () = 2 2

rS

⇒ 0 () = 22

59. () = 2

al

or ( + 2)( + 4) = 0, so = −2 or −4.

61. (a) () = + is continuous on R and (−1) = −1 − 1 0 1 = (0), so by the Intermediate Value Theorem,

+ = 0 has a root in (−1 0).

Fo

(b) () = + ⇒ 0 () = + 1, so +1 = −

+

. Using 1 = −05, we get 2 ≈ −0566311,

+ 1

3 ≈ −0567143 ≈ 4 , so the root is −0567143 to six decimal places.

63. (a) lim () = lim

→∞

1

1

= 1, since 0 ⇒ − → −∞ ⇒ − → 0.

=

1 + −

1+·0

⇒

N

(b) () = (1 + − )−1

(c)

−

= −(1 + − )−2 (−− ) =

(1 + − )2

ot

→∞

From the graph of () = (1 + 10−05 )−1 , it seems that () = 08

(indicating that 80% of the population has heard the rumor) when

≈ 74 hours.

65. () = −

⇒ 0 () = 1 − = 0 ⇔ = 1 ⇔ = 0. Now 0 () 0 for all 0 and 0 () 0 for all

0, so the absolute maximum value is (0) = 0 − 1 = −1.

2 8

67. () = −

, [−1 4]. 0 () = · −

2 8

· (− ) + −

4

2 8

2 8

· 1 = −

2

2 8

(− + 1). Since −

4

is never 0,

0 () = 0 ⇒ −2 4 + 1 = 0 ⇒ 1 = 2 4 ⇒ 2 = 4 ⇒ = ±2, but −2 is not in the given interval, [−1 4].

√

(−1) = −−18 ≈ −088, (2) = 2−12 ≈ 121, and (4) = 4−2 ≈ 054. So (2) = 2−12 = 2 is the absolute

√

maximum value and (−1) = −−18 = −1 8 is the absolute minimum value. c ° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

258

¤

CHAPTER 6 INVERSE FUNCTIONS

69. (a) () = (1 − )−

⇒ 0 () = (1 − )(−− ) + − (−1) = − ( − 2) 0 ⇒ 2, so is increasing on

(2 ∞) and decreasing on (−∞ 2).

(b) 00 () = − (1) + ( − 2)(−− ) = − (3 − ) 0 ⇔ 3, so is CU on (−∞ 3) and CD on (3 ∞).

(c) 00 changes sign at = 3, so there is an IP at 3 −2−3 .

71. = () = −1(+1)

C. No symmetry D.

−1 ( + 1) → −∞,

A. = { | 6= −1} = (−∞ −1) ∪ (−1, ∞) B. No -intercept; -intercept = (0) = −1

lim −1(+1) = 1 since −1( + 1) → 0, so = 1 is a HA.

→±∞

lim −1(+1) = ∞ since −1( + 1) → ∞, so = −1 is a VA.

→−1−

E. 0 () = −1(+1) ( + 1)2

⇒ 0 () 0 for all except 1, so

is increasing on (−∞ −1) and (−1 ∞). F. No extreme values

−1(+1)

−1(+1)

H.

−1(+1)

(−2)

+

=−

( + 1)4

( + 1)3

(2 + 1)

( + 1)4

e

G. 00 () =

lim −1(+1) = 0 since

→−1+

⇒

73. = 1(1 + − )

rS

al

00 () 0 ⇔ 2 + 1 0 ⇔ − 1 , so is CU on (−∞ −1)

2

and −1 − 1 , and CD on − 1 , ∞ . has an IP at − 1 , −2 .

2

2

2

A. = R B. No -intercept; -intercept = (0) = 1 C. No symmetry

2

D. lim 1(1 + − ) =

→∞

1

1+0

= 1 and lim 1(1 + − ) = 0 since lim − = ∞, so has horizontal asymptotes

→−∞

→−∞

F. No extreme values G. 00 () =

Fo

= 0 and = 1. E. 0 () = −(1 + − )−2 (−− ) = − (1 + − )2 . This is positive for all , so is increasing on R.

(1 + − )2 (−− ) − − (2)(1 + − )(−− )

− (− − 1)

=

(1 + − )4

(1 + − )3

The second factor in the numerator is negative for 0 and positive for 0,

H.

N

ot

and the other factors are always positive, so is CU on (−∞, 0) and CD

on (0 ∞). IP at 0, 1

2

75. () = − with = 001, = 4, and = 007. We will ﬁnd the

zeros of 00 for () = − .

0 () = (−− ) + − (−1 ) = − (− + −1 )

00 () = − (−−1 + ( − 1)−2 ) + (− + −1 )(−− )

= −2 − [− + ( − 1) + 2 2 − ]

= −2 − (2 2 − 2 + 2 − )

Using the given values of and gives us 00 () = 2 −007 (000492 − 056 + 12). So 00 () = 001 00 () and its zeros are = 0 and the solutions of 000492 − 056 + 12 = 0, which are 1 =

200

7

≈ 2857 and 2 =

600

7

≈ 8571.

At 1 minutes, the rate of increase of the level of medication in the bloodstream is at its greatest and at 2 minutes, the rate of decrease is the greatest. c ° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

SECTION 6.2 EXPONENTIAL FUNCTIONS AND THEIR DERIVATIVES

3

77. () =

−

¤

259

→ 0 as → −∞, and

() → ∞ as → ∞. From the graph,

it appears that has a local minimum of about (058) = 068, and a local maximum of about (−058) = 147.

To ﬁnd the exact values, we calculate

3

1

0 () = 32 − 1 − , which is 0 when 32 − 1 = 0 ⇔ = ± √3 . The negative root corresponds to the local

√ 3

√

√

1

maximum − √3 = (−1 3) − (−1 3) = 2 39 , and the positive root corresponds to the local minimum

1

√

3

= (1

3)3 − (1

√

3)

√

= −2

39

. To estimate the inﬂection points, we calculate and graph

3

3

3

3

2

3 − 1 − = 32 − 1 − 32 − 1 + − (6) = − 94 − 62 + 6 + 1 .

e

00 () =

√

From the graph, it appears that 00 () changes sign (and thus has inﬂection points) at ≈ −015 and ≈ −109. From the

1

( + ) =

0

81.

2

2

0

+1

+

+1

1

=

0

1

1

+ − (0 + 1) =

+−1

+1

+1

2

1

1

1

1

− = − − = − −2 + 0 = (1 − −2 )

0

83. Let = 1 + . Then = , so

85.

√

√

1 + =

= 2 32 + = 2 (1 + )32 + .

3

3

Fo

0

=

rS

79.

al

graph of , we see that these -values correspond to inﬂection points at about (−015 115) and (−109 082).

( + − )2 = (2 + 2 + −2 ) = 1 2 + 2 − 1 −2 +

2

2

tan sec2 =

ot

87. Let = tan . Then = sec2 , so

= + = tan + .

89. Let = 1, so = −12 . When = 1, = 1; when = 2, =

2

1

1

=

2

91. Area =

1

93. =

0

12

√

12

(−) = − 1 = −(12 − ) = − .

0

−2

1

1 3

1

− = 1 3 − 0 = 1 3 − − 1 − 1 = 1 3 − +

3

3

3

3

0

( )2 =

2

95. erf() = √

Thus,

N

1

2.

=

2

1

0

1

2 = 1 2 0 =

2

2

−

0

− =

0

0

−2

+

2

⇒

− −

0

2

− =

0

−2

2

2

3

≈ 4644

2

−1

√

erf() By Property 5 of deﬁnite integrals in Section 4.2,

2

, so

2

− =

√

√

erf() − erf() =

2

2

1

2

√

[erf() − erf()].

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

260

¤

CHAPTER 6 INVERSE FUNCTIONS

97. The rate is measured in liters per minute. Integrating from = 0 minutes to = 60 minutes will give us the total amount of oil

that leaks out (in liters) during the ﬁrst hour.

60

60

() = 0 100−001

[ = −001, = −001]

0

−06

−06

= 100 0

(−100 ) = −10,000 0

= −10,000(−06 − 1) ≈ 45119 ≈ 4512 liters

99. We use Theorem 6.1.7. Note that (0) = 3 + 0 + 0 = 4, so −1 (4) = 0. Also 0 () = 1 + . Therefore,

−1 0

(4) =

1

1

1

1

= .

= 0

=

0 ( −1 (4))

(0)

1 + 0

2

From the graph, it appears that is an odd function ( is undeﬁned for = 0).

101.

To prove this, we must show that (−) = −().

al

e

1

1 − 1 1

1 − 1(−)

1 − (−1)

1 − 1

(−) =

=

=

· 1 = 1

1(−)

(−1)

1

1+

1+

+1

1 + 1

1

1−

= −()

=−

1 + 1

rS

so is an odd function.

103. (a) Let () = − 1 − . Now (0) = 0 − 1 = 0, and for ≥ 0, we have 0 () = − 1 ≥ 0. Now, since (0) = 0 and

is increasing on [0 ∞), () ≥ 0 for ≥ 0 ⇒ − 1 − ≥ 0 ⇒ ≥ 1 + .

2

2

Fo

(b) For 0 ≤ ≤ 1, 2 ≤ , so ≤ [since is increasing]. Hence [from (a)] 1 + 2 ≤ ≤ .

1 2

1

1

1 2

So 4 = 0 1 + 2 ≤ 0 ≤ 0 = − 1 ⇒ 4 ≤ 0 ≤ .

3

3

2

+ ··· + for ≥ 0.

2!

!

ot

105. (a) By Exercise 103(a), the result holds for = 1. Suppose that ≥ 1 + +

2

+1

− ··· −

−

. Then 0 () = − 1 − − · · · −

≥ 0 by assumption. Hence

2!

!

( + 1)!

!

N

Let () = − 1 − −

() is increasing on (0 ∞). So 0 ≤ implies that 0 = (0) ≤ () = − 1 − − · · · −

≥ 1 + + · · · +

+1

−

, and hence

!

( + 1)!

2

+1

+ for ≥ 0. Therefore, for ≥ 0, ≥ 1 + +

+ ··· + for every positive

!

( + 1)!

2!

!

integer , by mathematical induction.

(b) Taking = 4 and = 1 in (a), we have = 1 ≥ 1 +

(c) ≥ 1 + + · · · +

+1

+

!

( + 1)!

⇒

1

2

+

1

6

+

1

24

= 27083 27.

1

1

1

+

≥

.

≥ + −1 + · · · +

!

( + 1)!

( + 1)!

= ∞, so lim = ∞.

→∞ ( + 1)!

→∞

But lim

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

SECTION 6.3

LOGARITHMIC FUNCTIONS

¤

6.3 Logarithmic Functions

1. (a) It is deﬁned as the inverse of the exponential function with base , that is, log =

(b) (0 ∞)

(c) R

⇔ = .

(d) See Figure 1.

1

1

1

= −3 since 3−3 = 3 =

.

27

3

27

3. (a) log5 125 = 3 since 53 = 125.

(b) log3

5. (a) ln 45 = 45 since ln = for 0.

(b) log10 00001 = log10 10−4 = −4 by (2).

6

7. (a) log2 6 − log2 15 + log2 20 = log2 ( 15 ) + log2 20

[by Law 2]

[by Law 1]

6

= log2 ( 15 · 20)

= log2 8, and log2 8 = 3 since 23 = 8.

11. ln

1

2

ln() = 1 (ln + ln ) =

2

1

2

al

√

= ln()12 =

18

ln +

1

2

ln [assuming that the variables are positive]

rS

9. ln

100

e

100

− log3 50 = log3 18·50

= log3 ( 1 ), and log3 1 = −2 since 3−2 = 1

9

9

9

(b) log3 100 − log3 18 − log3 50 = log3

2

= ln 2 − ln( 3 4 ) = 2 ln − (ln 3 + ln 4 ) = 2 ln − 3 ln − 4 ln

3 4

13. 2 ln + 3 ln − ln = ln 2 + ln 3 − ln

2 3

= ln

15. ln 5 + 5 ln 3 = ln 5 + ln 35

[by Law 1]

Fo

= ln( ) − ln

[by Law 3]

2 3

[by Law 3]

[by Law 1]

ot

5

[by Law 2]

= ln(5 · 3 )

= ln 1215

1

3

ln − ln(2 + 3 + 2)2 = ln[( + 2)3 ]13 +

N

17.

ln( + 2)3 +

1

2

= ln( + 2) + ln

1

2

ln

(2 + 3 + 2)2

√

2 + 3 + 2

√

( + 2)

( + 1)( + 2)

√

= ln

+1

= ln

[by Laws 3, 2]

[by Law 3]

[by Law 1]

Note that since ln is deﬁned for 0, we have + 1, + 2, and 2 + 3 + 2 all positive, and hence their logarithms are deﬁned.

1

ln

=

≈ 0402430 ln 12 ln 12 ln

(c) log2 =

≈ 1651496 ln 2

19. (a) log12 =

(b) log6 1354 =

ln 1354

≈ 1454240 ln 6

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

261

262

¤

CHAPTER 6

INVERSE FUNCTIONS

21. To graph these functions, we use log15 =

ln ln and log50 =

.

ln 15 ln 50

These graphs all approach −∞ as → 0+ , and they all pass through the

point (1 0). Also, they are all increasing, and all approach ∞ as → ∞.

The functions with larger bases increase extremely slowly, and the ones with smaller bases do so somewhat more quickly. The functions with large bases approach the -axis more closely as → 0+ .

23. (a) Shift the graph of = log10 ﬁve units to the left to

(b) Reﬂect the graph of = ln about the -axis to obtain the graph of = − ln .

obtain the graph of = log10 ( + 5). Note the vertical

= log10 ( + 5)

= ln

= − ln

rS

= log10

al

e

asymptote of = −5.

25. (a) The domain of () = ln + 2 is 0 and the range is R.

(b) = 0 ⇒ ln + 2 = 0 ⇒ ln = −2 ⇒ = −2

⇔

7 − 4 = ln 6

(b) ln(3 − 10) = 2

29. (a) 2−5 = 3

⇔

⇔

3 − 10 = 2

7 − ln 6 = 4

⇔

⇔

3 = 2 + 10

ot

27. (a) 7−4 = 6

Fo

(c) We shift the graph of = ln two units upward.

= 1 (7 − ln 6)

4

⇔

= 1 (2 + 10)

3

⇔ log2 3 = − 5 ⇔ = 5 + log2 3.

N

ln 3

Or: 2−5 = 3 ⇔ ln 2−5 = ln 3 ⇔ ( − 5) ln 2 = ln 3 ⇔ − 5 = ln 2

⇔ =5+

ln 3 ln 2

(b) ln + ln( − 1) = ln(( − 1)) = 1 ⇔ ( − 1) = 1 ⇔ 2 − − = 0. The quadratic formula (with = 1,

√

= −1, and = −) gives = 1 1 ± 1 + 4 , but we reject the negative root since the natural logarithm is not

2

√ deﬁned for 0. So = 1 1 + 1 + 4 .

2

31. − −2 = 1

33. ln(ln ) = 1

⇔ − 1 = −2

⇔ ln(ln ) = 1

35. 2 − − 6 = 0

37. (a) 2+5 = 100

⇔ ln( − 1) = ln −2

⇔ −2 = ln( − 1) ⇔ = − 1 ln( − 1)

2

⇔ ln = 1 = ⇔ ln =

⇔ =

⇔ ( − 3)( + 2) = 0 ⇔ = 3 or −2 ⇒ = ln 3 since 0.

⇒ ln 2+5 = ln 100 ⇒ 2 + 5 = ln 100 ⇒ 5 = ln 100 − 2 ⇒

= 1 (ln 100 − 2) ≈ 05210

5

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

SECTION 6.3

(b) ln( − 2) = 3 ⇒ − 2 = 3

39. (a) ln 0

⇒ 0

is 0 1.

LOGARITHMIC FUNCTIONS

¤

263

⇒ = 3 + 2 ⇒ = ln(3 + 2) ≈ 30949

⇒ 1. Since the domain of () = ln is 0, the solution of the original inequality

(b) 5 ⇒ ln ln 5 ⇒ ln 5

41. 3 ft = 36 in, so we need such that log2 = 36

68,719,476,736 in ·

⇔ = 236 = 68,719,476,736. In miles, this is

1 ft

1 mi

·

≈ 1,084,5877 mi.

12 in 5280 ft

43. If is the intensity of the 1989 San Francisco earthquake, then log10 () = 71

log10 (16) = log10 16 + log10 () = log10 16 + 71 ≈ 83.

45. (a) = () = 100 · 23 ⇒

= 23 ⇒ log2

=

100

100

3

⇒ = 3 log2

. Using formula (7), we can

100

ln(100)

. This function tells us how long it will take to obtain bacteria (given the ln 2

e

write this as = −1 () = 3 ·

⇒

ln 50,000 ln 500

100

=3

≈ 269 hours ln 2 ln 2

rS

(b) = 50,000 ⇒ = −1 (50,000) = 3 ·

al

number ).

47. Let = 2 − 9. Then as → 3+ , → 0+ , and lim ln(2 − 9) = lim ln = −∞ by (8).

→3+

→0+

49. lim ln(cos ) = ln 1 = 0. [ln(cos ) is continuous at = 0 since it is the composite of two continuous functions.]

Fo

→0

51. lim [ln(1 + 2 ) − ln(1 + )] = lim ln

→∞

→∞

parentheses is ∞.

1 + 2

→∞ 1 + lim

= ln

1

→∞ 1

lim

+

+1

= | 2 − 9 0 = || 3 = (−∞ −3) ∪ (3 ∞)

√

3 − 2 , we must have 3 − 2 ≥ 0 ⇒ 2 ≤ 3

N

55. (a) For () =

ot

53. () = log10 (2 − 9).

1 + 2

= ln

1+

⇒

= ∞, since the limit in

2 ≤ ln 3 ⇒ ≤

1

2

ln 3.

Thus, the domain of is (−∞ 1 ln 3].

2

(b) = () =

√

3 − 2

[note that ≥ 0] ⇒ 2 = 3 − 2

⇒ 2 = 3 − 2

⇒ 2 = ln(3 − 2 ) ⇒

ln(3 − 2 ). So −1 () = 1 ln(3 − 2 ). For the domain of −1 ,

2

√

√

√

√

2

2

we must have 3 − 0 ⇒ 3 ⇒ || 3 ⇒ − 3 3 ⇒ 0 ≤ 3 since ≥ 0. Note

√

that the domain of −1 , [0 3 ), equals the range of .

=

1

2

ln(3 − 2 ). Interchange and : =

57. (a) We must have − 3 0

1

2

⇒ 3 ⇒ ln 3. Thus, the domain of () = ln( − 3) is (ln 3 ∞).

(b) = ln( − 3) ⇒ = − 3 ⇒ = + 3 ⇒ = ln( + 3), so −1 () = ln( + 3).

Now + 3 0 ⇒ −3, which is true for any real , so the domain of −1 is R.

59. = ln( + 3)

⇒ = ln(+3) = + 3 ⇒ = − 3.

Interchange and : the inverse function is = − 3.

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

264

¤

CHAPTER 6 INVERSE FUNCTIONS

61. = () =

3

63. = log10 1 +

⇒ ln = 3

1

⇒ 10 = 1 +

Interchange and : =

1

3

1

√

√

√

3

ln . Interchange and : = 3 ln . So −1 () = 3 ln .

⇒

1

1

= 10 − 1 ⇒ =

.

10 − 1

1 is the inverse function.

10 − 1

33

1

1

1

⇔ 2 ln 3 = − ln 3 ⇔ − 2 ln 3, so is increasing on − 2 ln 3 ∞ .

65. () = 3 −

2

⇒ =

⇒ 0 () = 33 − . Thus, 0 () 0

⇔

33

⇔

⇔ 32 1 ⇔

67. (a) We have to show that − () = (−).

√

√

−1

− () = − ln + 2 + 1 = ln + 2 + 1

= ln

1

√

2 + 1

√

√

√

1

− 2 + 1

− 2 + 1

√

√

= ln 2 + 1 − = (−)

·

= ln 2

= ln

2 +1

2 +1

− 2 − 1

+

−

e

+

al

Thus, is an odd function.

2 = 2 − 1 ⇔ =

2 − 1

= 1 ( − − ). Thus, the inverse function is −1 () = 1 ( − − ).

2

2

2

1

· ln = ln 2 ⇒ 1 = ln 2, a contradiction, so the given equation has no ln

⇒ ln(1 ln ) = ln(2) ⇒

Fo

69. 1 ln = 2

rS

√

√

(b) Let = ln + 2 + 1 . Then = + 2 + 1 ⇔ ( − )2 = 2 + 1 ⇔ 2 − 2 + 2 = 2 + 1 ⇔

solution. The function () = 1 ln = (ln )1 ln = 1 = for all 0, so the function () = 1 ln is the constant function () = .

71. (a) Let 0 be given. We need such that | − 0| when . But

Then

ot

→−∞

(b) Let 0 be given. We need such that when . But

⇒ log

⇔ log . Let = log .

⇒ , so lim = ∞.

N

Then

⇔ log . Let = log .

⇒ log ⇒ | − 0| = , so lim = 0.

→∞

⇒ 0 2 − 2 − 2 ≤ 1. Now 2 − 2 − 2 ≤ 1 gives 2 − 2 − 3 ≤ 0 and hence

√

√

( − 3)( + 1) ≤ 0. So −1 ≤ ≤ 3. Now 0 2 − 2 − 2 ⇒ 1 − 3 or 1 + 3. Therefore,

√

√ ln(2 − 2 − 2) ≤ 0 ⇔ −1 ≤ 1 − 3 or 1 + 3 ≤ 3.

73. ln(2 − 2 − 2) ≤ 0

6.4 Derivatives of Logarithmic Functions

1. The differentiation formula for logarithmic functions,

3. () = sin(ln )

⇒ 0 () = cos(ln ) ·

1

(log ) =

, is simplest when = because ln = 1.

ln

1

cos(ln ) ln = cos(ln ) · =

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

SECTION 6.4 DERIVATIVES OF LOGARITHMIC FUNCTIONS

5. () = ln

¤

1

Another solution: () = ln

7. () = log10 (3 + 1)

9. () = sin ln(5)

1

1

= ln 1 − ln = − ln ⇒ 0 () = − .

⇒ 0 () =

(3

3

1

32

( + 1) = 3

+ 1) ln 10

( + 1) ln 10

⇒ 0 () = sin ·

sin · 5 sin

1

·

(5) + ln(5) · cos =

+ cos ln(5) =

+ cos ln(5)

5

5

(2 + 1)5

= ln(2 + 1)5 − ln( 2 + 1)12 = 5 ln(2 + 1) − 1 ln( 2 + 1) ⇒

2

2 + 1

1

1

10

8 2 − + 10

1

0 () = 5 ·

·2− · 2

· 2 =

− 2 or 2 + 1

2 +1

2 + 1 + 1

(2 + 1)(2 + 1)

1

1

1

2 − 1 + ·

22 − 1

1

+ · 2

· 2 = + 2

=

=

2 − 1)

2 −1

−1

(

(2 − 1) ln

1 + ln(2)

⇒

1

[1 + ln(2)] · − ln ·

[1 + ln(2)]2

17. () = 5 + 5

1

2

·2

=

rS

0 () =

ln(2 − 1) ⇒

1

[1

+ ln(2) − ln ]

1 + (ln 2 + ln ) − ln

1 + ln 2

=

=

[1 + ln(2)]2

[1 + ln(2)]2

[1 + ln(2)]2

Fo

15. () =

1

2

al

√

2 − 1 = ln + ln(2 − 1)12 = ln +

13. () = ln

e

11. () = ln

0 () =

⇒ 0 () = 54 + 5 ln 5

⇒ 0 = sec2 [ln( + )] ·

1

· = sec2 [ln( + )]

+

+

ot

19. = tan [ln( + )]

21. = ln(− + − ) = ln(− (1 + )) = ln(− ) + ln(1 + ) = − + ln(1 + )

23. = 2 log10

Note:

⇒

−1 − + 1

1

=

=−

1+

1+

1+

N

0 = −1 +

√

= 2 log10 12 = 2 ·

1

2

log10 = log10 ⇒ 0 = ·

1

1

+ log10 · 1 =

+ log10

ln 10 ln 10

1 ln

1

=

= log10 , so the answer could be written as

+ log10 = log10 + log10 = log10 . ln 10 ln 10 ln 10

√

25. () = 10

265

1 1

1

1

⇒ 0 () =

= − 2 =− .

1

27. = 2 ln(2)

00 = 1 + 2 ·

√

⇒ 0 () = 10

⇒ 0 = 2 ·

√

ln 10

√ 10 ln 10

√

=

2

1

· 2 + ln(2) · (2) = + 2 ln(2) ⇒

2

1

· 2 + ln(2) · 2 = 1 + 2 + 2 ln(2) = 3 + 2 ln(2)

2

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

266

¤

CHAPTER 6 INVERSE FUNCTIONS

29. = ln +

√

⇒

1 + 2

√

1

1

√

√

1 + 1 (1 + 2 )−12 (2)

+ 1 + 2 =

2

2

2

+ 1+

+ 1+

√

1 + 2 +

1

1

1

√

√

1+ √

=

· √

= √

=

2

2

2

2

+ 1+

1+

+ 1+

1+

1 + 2

00 = − 1 (1 + 2 )−32 (2) =

2

31. () =

0

() =

−

(1 + 2 )32

⇒

−1

( − 1)[1 − ln( − 1)] +

− 1 − ( − 1) ln( − 1) +

−1 =

−1

=

[1 − ln( − 1)]2

( − 1)[1 − ln( − 1)]2

[1 − ln( − 1)]2

[1 − ln( − 1)] · 1 − ·

2 − 1 − ( − 1) ln( − 1)

( − 1)[1 − ln( − 1)]2

al

=

1 − ln( − 1)

⇒

e

0 =

33. () = ln(2 − 2)

⇒ 0 () =

rS

Dom() = { | − 1 0 and 1 − ln( − 1) 6= 0} = { | 1 and ln( − 1) 6= 1}

= | 1 and − 1 6= 1 = { | 1 and 6= 1 + } = (1 1 + ) ∪ (1 + ∞)

2( − 1)

1

(2 − 2) =

.

2 − 2

( − 2)

Dom( ) = { | ( − 2) 0} = (−∞ 0) ∪ (2 ∞).

37. = ln(2 − 3 + 1)

⇒

0 =

Fo

ln

1 + 2

1

· (2 − 3)

2 − 3 + 1

⇒

0 (3) =

1

1

· 3 = 3, so an equation of a tangent line at

ot

35. () =

1

(1 + 2 )

− (ln )(2)

1

2(1) − 0(2)

2

0

⇒ () =

, so 0 (1) =

= = .

(1 + 2 )2

22

4

2

(3 0) is − 0 = 3( − 3), or = 3 − 9.

⇒ 0 () = cos + 1.

N

39. () = sin + ln

This is reasonable, because the graph shows that increases when 0 is positive, and 0 () = 0 when has a horizontal tangent.

41. () = + ln(cos )

0( ) = 6

4

⇒

⇒

0 () = +

− tan = 6

4

⇒

1

· (− sin ) = − tan . cos

−1 =6

⇒

= 7.

43. = (2 + 2)2 (4 + 4)4

⇒ ln = ln[(2 + 2)2 (4 + 4)4 ] ⇒ ln = 2 ln(2 + 2) + 4 ln(4 + 4) ⇒

1

4

1

163

1 0

=2· 2

· 2 + 4 · 4

· 43 ⇒ 0 = 2

+ 4

⇒

+2

+4

+2

+4

4

163

+ 4

0 = (2 + 2)2 (4 + 4)4

2 + 2

+4 c ° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

¤

SECTION 6.4 DERIVATIVES OF LOGARITHMIC FUNCTIONS

45. =

12

−1

⇒ ln = ln 4

+1

−1

4 + 1

1 0

1 1

1 1

=

−

· 43

2−1

2 4 + 1

47. =

⇒ ln = ln

267

1

1

ln( − 1) − ln(4 + 1) ⇒

2

2

1

1

−1

23

23

− 4

⇒ 0 =

− 4

⇒ 0 =

2( − 1)

+1

4 + 1 2 − 2

+1

⇒ ln =

⇒ ln = ln ⇒ 0 = (1) + (ln ) · 1 ⇒ 0 = (1 + ln ) ⇒

0 = (1 + ln )

49. = sin

0 =

⇒ ln = ln sin

sin

+ ln cos

51. = (cos )

⇒

1

0

= (sin ) · + (ln )(cos ) ⇒

sin

0 = sin

+ ln cos

⇒

⇒ ln = ln(cos )

ln = sin ln ⇒

1 0

1

=·

· (− sin ) + ln cos · 1 ⇒

cos

⇒ ln = ln cos ⇒

al

e

sin

0 = ln cos −

⇒ 0 = (cos ) (ln cos − tan ) cos

1 ln tan ⇒

sec2

1 0

1

ln tan

1

1

= ·

· sec2 + ln tan · − 2

−

⇒ 0 =

⇒

tan

tan

2

sec2 ln tan ln tan

1

or 0 = (tan )1 ·

−

csc sec −

0 = (tan )1

tan

2

55. = ln(2 + 2 )

⇒ 0 =

⇒ ln =

rS

⇒ ln = ln(tan )1

Fo

53. = (tan )1

2

1

2 + 2 0

(2 + 2 ) ⇒ 0 = 2

2

+

+ 2

ot

2 0 + 2 0 − 2 0 = 2 ⇒ (2 + 2 − 2) 0 = 2 ⇒ 0 =

⇒ 0 () =

N

57. () = ln( − 1)

(4) () = −2 · 3( − 1)−4

59.

1

= ( − 1)−1

( − 1)

⇒ ···

⇒ 2 0 + 2 0 = 2 + 2 0

⇒

2

2 + 2 − 2

⇒ 00 () = −( − 1)−2

⇒ 000 () = 2( − 1)−3

⇒ () () = (−1)−1 · 2 · 3 · 4 · · · · · ( − 1)( − 1)− = (−1)−1

⇒

( − 1)!

( − 1)

From the graph, it appears that the curves = ( − 4)2 and = ln intersect just to the left of = 3 and to the right of = 5, at about = 53. Let

() = ln − ( − 4)2 . Then 0 () = 1 − 2( − 4), so Newton’s Method says that +1 = − ( ) 0 ( ) = −

ln − ( − 4)2

. Taking

1 − 2( − 4)

0 = 3, we get 1 ≈ 2957738, 2 ≈ 2958516 ≈ 3 , so the ﬁrst root is 2958516, to six decimal places. Taking 0 = 5, we get 1 ≈ 5290755, 2 ≈ 5290718 ≈ 3 , so the second (and ﬁnal) root is 5290718, to six decimal places.

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

268

¤

CHAPTER 6 INVERSE FUNCTIONS

ln

61. () = √

⇒ 0 () =

√

√

(1) − (ln )[1(2 )]

2 − ln

=

232

⇒

232 (−1) − (2 − ln )(312 )

3 ln − 8

=

0 ⇔ ln

43

452

and CD on (0 83 ). The inﬂection point is 83 8 −43 .

3

00 () =

8

3

⇔ 83 , so is CU on (83 ∞)

63. = () = ln(sin )

A. = { in R | sin 0} =

∞

=−∞

(2 (2 + 1) ) = · · · ∪ (−4 −3) ∪ (−2 −) ∪ (0 ) ∪ (2 3) ∪ · · ·

B. No -intercept; -intercepts: () = 0 ⇔ ln(sin ) = 0 ⇔ sin = 0 = 1 ⇔ integer .

C. is periodic with period 2. D.

lim

→(2)+

() = −∞ and

lim

→[(2+1)]−

= 2 +

2

for each

() = −∞, so the lines

cos

= cot , so 0 () 0 when 2 2 + for each

2

sin

(2 + 1). Thus, is increasing on 2 2 + and

2

al

H.

rS

integer , and 0 () 0 when 2 +

2

decreasing on 2 + 2 (2 + 1) for each integer .

F. Local maximum values 2 + = 0, no local minimum.

2

e

= are VAs for all integers . E. 0 () =

G. 00 () = − csc2 0, so is CD on (2 (2 + 1)) for

Fo

each integer No IP

A. = R B. Both intercepts are 0 C. (−) = (), so the curve is symmetric about the

65. = () = ln(1 + 2 )

-axis. D.

lim ln(1 + 2 ) = ∞, no asymptotes. E. 0 () =

→±∞

2

0 ⇔

1 + 2

H.

ot

0, so is increasing on (0 ∞) and decreasing on (−∞ 0)

F. (0) = 0 is a local and absolute minimum.

2(1 + 2 ) − 2(2)

2(1 − 2 )

=

0 ⇔

2 )2

(1 +

(1 + 2 )2

N

G. 00 () =

|| 1, so is CU on (−1 1), CD on (−∞ −1) and (1 ∞).

IP (1 ln 2) and (−1 ln 2).

67. We use the CAS to calculate 0 () =

00 () =

2 + sin + cos and 2 + sin

22 sin + 4 sin − cos2 + 2 + 5

. From the graphs, it

2 (cos2 − 4 sin − 5)

seems that 0 0 (and so is increasing) on approximately the intervals

(0 27), (45 82) and (109 143). It seems that 00 changes sign

(indicating inﬂection points) at ≈ 38, 57, 100 and 120.

Looking back at the graph of () = ln(2 + sin ), this implies that the inﬂection points have approximate coordinates

(38 17), (57 21), (100 27), and (120 29). c ° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

SECTION 6.4 DERIVATIVES OF LOGARITHMIC FUNCTIONS

¤

269

69. (a) Using a calculator or CAS, we obtain the model = with ≈ 1000124369 and ≈ 0000045145933.

(b) Use 0 () = ln (from Formula 7) with the values of and from part (a) to get 0 (004) ≈ −67063 A.

The result of Example 2 in Section 1.4 was −670 A.

71.

4

2

73.

2

1

3

= 3

4

2

4

1

4

= 3 ln || = 3(ln 4 − ln 2) = 3 ln = 3 ln 2

2

2

2

1

1

1

1

1 5

= − ln |8 − 3| = − ln 2 − − ln 5 = (ln 5 − ln 2) = ln

8 − 3

3

3

3

3

3 2

1

Or: Let = 8 − 3. Then = −3 , so

2

2 1

2

− 3

1

1

1

1 5

1

=

= − ln || = − ln 2 − − ln 5 = (ln 5 − ln 2) = ln .

3

3

3

3

3 2

1 8 − 3

5

5

1

1 2

2

=

77. Let = ln . Then =

79.

+−

⇒

1

2

(ln )2

=

2 =

1 3

1

+ = (ln )3 + .

3

3

sin 2 sin cos

= 2

= 2. Let = cos . Then = − sin , so

1 + cos2

1 + cos2

2 = −2

= −2 · 1 ln(1 + 2 ) + = − ln(1 + 2 ) + = − ln(1 + cos2 ) + .

2

1 + 2

Or: Let = 1 + cos2 .

2

10 =

1

10 ln 10

2

=

1

101

100 − 10

90

102

−

=

=

ln 10 ln 10 ln 10 ln 10

ot

81.

1

+1+

= 1 2 + + ln 1 = 1 2 + + 1 − 1 + 1 + 0

2

2

2

e

al

1

2 + + 1

=

rS

Fo

75.

1

(ln |sin | + ) = cos = cot

sin

cos

(b) Let = sin . Then = cos , so cot =

=

= ln || + = ln |sin | + . sin

N

83. (a)

√

85. The cross-sectional area is 1 + 1

0

1

2

= ( + 1). Therefore, the volume is

= [ln( + 1)]1 = (ln 2 − ln 1) = ln 2.

0

+1

87. =

2

1

=

1000

600

=

1000

600

1000

1

= ln | |

= (ln 1000 − ln 600) = ln 1000 = ln 5 .

600

3

600

Initially, = , where = 150 kPa and = 600 cm3 , so = (150)(600) = 90,000. Thus,

= 90 000 ln 5 ≈ 45 974 kPa · cm3 = 45 974(103 Pa)(10−6 m3 ) = 45 974 Pa·m3 = 45 974 N·m [Pa = Nm2 ]

3

= 45 974 J

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

270

¤

CHAPTER 6 INVERSE FUNCTIONS

⇒ 0 () = 2 + 1. If = −1 , then (1) = 2 ⇒ (2) = 1, so

89. () = 2 + ln

0 (2) = 1 0 ((2)) = 1 0 (1) = 1 .

3

91. The curve and the line will determine a region when they intersect at two or

more points. So we solve the equation (2 + 1) = ⇒ = 0 or

± −4()( − 1)

1

2

=±

− 1.

+ − 1 = 0 ⇒ = 0 or =

2

Note that if = 1, this has only the solution = 0, and no region is determined. But if 1 − 1 0 ⇔ 1 1 ⇔ 0 1, then there are two solutions. [Another way of seeing this is to observe that the slope of the tangent to = (2 + 1) at the origin is 0 = 1 and therefore we must have 0 1.]

Note that we cannot just integrate between the positive and negative roots, since the curve and the line cross at the origin.

93. If () = ln (1 + ), then 0 () =

Thus, lim

1

, so 0 (0) = 1.

1+

ln(1 + )

()

() − (0)

= lim

= lim

= 0 (0) = 1.

→0

→0

−0

ot

→0

rS

0

√1−1

− = 2 1 ln(2 + 1) − 1 2 0

2

2

2 + 1

1

1

−1+1 −

−1

− (ln 1 − 0)

= ln

1

= ln

+ − 1 = − ln − 1

Fo

2

√1−1

al

e

Since and (2 + 1) are both odd functions, the total area is twice the area between the curves on the interval

0 1 − 1 . So the total area enclosed is

N

6.2* The Natural Logarithmic Function

1. ln

√

= ln()12 =

3. ln

2

= ln 2 − ln( 3 4 ) = 2 ln − (ln 3 + ln 4 ) = 2 ln − 3 ln − 4 ln

3 4

1

2

ln() = 1 (ln + ln ) =

2

5. 2 ln + 3 ln − ln = ln 2 + ln 3 − ln

= ln(2 3 ) − ln

1

2

ln +

1

2

ln [assuming that the variables are positive]

[by Law 3]

[by Law 1]

2 3

= ln

7. ln 5 + 5 ln 3 = ln 5 + ln 35

5

= ln(5 · 3 )

[by Law 2]

[by Law 3]

[by Law 1]

= ln 1215

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

SECTION 6.2* THE NATURAL LOGARITHMIC FUNCTION

9.

1

3

ln( + 2)3 +

1

2

ln − ln(2 + 3 + 2)2 = ln[( + 2)3 ]13 +

= ln( + 2) + ln

1

2

ln

(2 + 3 + 2)2

√

2 + 3 + 2

√

( + 2)

( + 1)( + 2)

√

= ln

+1

¤

271

[by Laws 3, 2]

[by Law 3]

[by Law 1]

= ln

Note that since ln is deﬁned for 0, we have + 1, + 2, and 2 + 3 + 2 all positive, and hence their logarithms are deﬁned.

13.

11. Reﬂect the graph of = ln about the -axis to obtain

al

e

the graph of = − ln .

= ln( + 3)

rS

= ln

= ln

= − ln

15. Let = 2 − 9. Then as → 3+ , → 0+ , and lim ln(2 − 9) = lim ln = −∞ by (4).

17. () =

Fo

→3+

√

ln ⇒ 0 () =

1

⇒ 0 () =

1

1

N

21. () = ln

⇒ 0 () = cos(ln ) ·

Another solution: () = ln

23. () = sin ln(5)

25. () = ln

0 () =

1

ln + 2

√

=

2

1 cos(ln )

ln = cos(ln ) · =

ot

19. () = sin(ln )

√

1

√ ln +

2

→0+

1

1

1

= − 2 =− .

1

1

= ln 1 − ln = − ln ⇒ 0 () = − .

⇒ 0 () = sin ·

sin · 5 sin

1

·

(5) + ln(5) · cos =

+ cos ln(5) =

+ cos ln(5)

5

5

−

= ln( − ) − ln( + ) ⇒

+

−( + ) − ( − )

1

1

−2

(−1) −

=

= 2

−

+

( − )( + )

− 2

(2 + 1)5

= ln(2 + 1)5 − ln( 2 + 1)12 = 5 ln(2 + 1) − 1 ln( 2 + 1) ⇒

2

2 + 1

1

1

10

8 2 − + 10

1

·2− · 2

· 2 =

− 2 or 0 () = 5 ·

2 + 1

2 +1

2 + 1 + 1

(2 + 1)(2 + 1)

27. () = ln

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

¤

CHAPTER 6 INVERSE FUNCTIONS

√

2 − 1 = ln + ln(2 − 1)12 = ln +

29. () = ln

0 () =

31. () =

0 () =

ln

1 + ln(2)

⇒

1

[1 + ln(2)] · − ln ·

[1 + ln(2)]2

1

2

·2

=

1

[1

+ ln(2) − ln ]

1 + (ln 2 + ln ) − ln

1 + ln 2

=

=

[1 + ln(2)]2

[1 + ln(2)]2

[1 + ln(2)]2

1

−10 − 1

10 + 1

· (−1 − 10) = or 2 − − 52

2 − − 52

52 + − 2

⇒ 0 =

35. = tan [ln( + )]

⇒ 0 = sec2 [ln( + )] ·

⇒ 0 = 2 ·

37. = 2 ln(2)

=

1

· 2 + ln(2) · (2) = + 2 ln(2) ⇒

2

1 − ln( − 1)

al

1

· 2 + ln(2) · 2 = 1 + 2 + 2 ln(2) = 3 + 2 ln(2)

2

⇒

−1

( − 1)[1 − ln( − 1)] +

− 1 − ( − 1) ln( − 1) +

−1 =

−1

=

[1 − ln( − 1)]2

( − 1)[1 − ln( − 1)]2

[1 − ln( − 1)]2

[1 − ln( − 1)] · 1 − ·

2 − 1 − ( − 1) ln( − 1)

( − 1)[1 − ln( − 1)]2

Fo

() =

1

· = sec2 [ln( + )]

+

+

rS

00 = 1 + 2 ·

0

ln(2 − 1) ⇒

1

1

1

1

2 − 1 + ·

22 − 1

+ · 2

· 2 = + 2

=

=

2 − 1)

2 −1

−1

(

(2 − 1)

33. = ln 2 − − 52

39. () =

1

2

e

272

√

1 − ln is deﬁned ⇔ 0 [so that ln is deﬁned] and 1 − ln ≥ 0 ⇔

N

41. () =

ot

Dom() = { | − 1 0 and 1 − ln( − 1) 6= 0} = { | 1 and ln( − 1) 6= 1}

= | 1 and − 1 6= 1 = { | 1 and 6= 1 + } = (1 1 + ) ∪ (1 + ∞)

0 and ln ≤ 1 ⇔ 0 ≤ , so the domain of is (0 ]. Now

1

1

1

−1

√

0 () = (1 − ln )−12 ·

· −

.

(1 − ln ) = √

=

2

2 1 − ln

2 1 − ln

43. () =

ln

1 + 2

1

− (ln )(2)

(1 + 2 )

2(1) − 0(2)

2

1

0

⇒ () =

, so 0 (1) =

= = .

(1 + 2 )2

22

4

2

45. () = sin + ln

⇒ 0 () = cos + 1.

This is reasonable, because the graph shows that increases when 0 is positive, and 0 () = 0 when has a horizontal tangent.

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

¤

SECTION 6.2* THE NATURAL LOGARITHMIC FUNCTION

⇒ 0 = cos(2 ln ) ·

47. = sin(2 ln )

273

2

2

. At (1 0), 0 = cos 0 · = 2, so an equation of the tangent line is

1

− 0 = 2 · ( − 1), or = 2 − 2.

49. = ln(2 + 2 )

⇒ 0 =

2

1

2 + 2 0

(2 + 2 ) ⇒ 0 = 2

2

+

+ 2

⇒ 0 () =

(4) () = −2 · 3( − 1)−4

1

= ( − 1)−1

( − 1)

⇒ ···

⇒

2

2 + 2 − 2

2 0 + 2 0 − 2 0 = 2 ⇒ (2 + 2 − 2) 0 = 2 ⇒ 0 =

51. () = ln( − 1)

⇒ 2 0 + 2 0 = 2 + 2 0

⇒ 00 () = −( − 1)−2

⇒ 000 () = 2( − 1)−3

⇒ () () = (−1)−1 · 2 · 3 · 4 · · · · · ( − 1)( − 1)− = (−1)−1

⇒

( − 1)!

( − 1)

From the graph, it appears that the curves = ( − 4)2 and = ln intersect

e

53.

just to the left of = 3 and to the right of = 5, at about = 53. Let

al

() = ln − ( − 4)2 . Then 0 () = 1 − 2( − 4), so Newton’s Method

rS

says that +1 = − ( ) 0 ( ) = −

ln − ( − 4)2

. Taking

1 − 2( − 4)

0 = 3, we get 1 ≈ 2957738, 2 ≈ 2958516 ≈ 3 , so the ﬁrst root is 2958516, to six decimal places. Taking 0 = 5, we

55. = () = ln(sin )

Fo

get 1 ≈ 5290755, 2 ≈ 5290718 ≈ 3 , so the second (and ﬁnal) root is 5290718, to six decimal places.

A. = { in R | sin 0} =

∞

=−∞

(2 (2 + 1) ) = · · · ∪ (−4 −3) ∪ (−2 −) ∪ (0 ) ∪ (2 3) ∪ · · ·

integer .

ot

B. No -intercept; -intercepts: () = 0 ⇔ ln(sin ) = 0 ⇔ sin = 0 = 1 ⇔

C. is periodic with period 2. D.

lim

→(2)+

() = −∞ and

lim

→[(2+1)]−

= 2 +

2

for each

() = −∞, so the lines

cos

= cot , so 0 () 0 when 2 2 + for each

2

sin

(2 + 1). Thus, is increasing on 2 2 + and

2

N

= are VAs for all integers . E. 0 () =

integer , and 0 () 0 when 2 +

2

decreasing on 2 + (2 + 1) for each integer .

2

F. Local maximum values 2 + = 0, no local minimum.

2

H.

G. 00 () = − csc2 0, so is CD on (2 (2 + 1)) for each integer No IP

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

¤

274

CHAPTER 6 INVERSE FUNCTIONS

A. = R B. Both intercepts are 0 C. (−) = (), so the curve is symmetric about the

57. = () = ln(1 + 2 )

-axis. D.

lim ln(1 + 2 ) = ∞, no asymptotes. E. 0 () =

→±∞

2

0 ⇔

1 + 2

H.

0, so is increasing on (0 ∞) and decreasing on (−∞ 0)

F. (0) = 0 is a local and absolute minimum.

G. 00 () =

2(1 + 2 ) − 2(2)

2(1 − 2 )

=

0 ⇔

2 )2

(1 +

(1 + 2 )2

|| 1, so is CU on (−1 1), CD on (−∞ −1) and (1 ∞).

IP (1 ln 2) and (−1 ln 2).

00 () =

2 + sin + cos and 2 + sin

22 sin + 4 sin − cos2 + 2 + 5

. From the graphs, it

2 (cos2 − 4 sin − 5)

(0 27), (45 82) and (109 143). It seems that 00 changes sign

rS

(indicating inﬂection points) at ≈ 38, 57, 100 and 120.

al

seems that 0 0 (and so is increasing) on approximately the intervals

e

59. We use the CAS to calculate 0 () =

Looking back at the graph of () = ln(2 + sin ), this implies that the inﬂection points have approximate coordinates

(38 17), (57 21), (100 27), and (120 29).

⇒ ln = ln[(2 + 2)2 (4 + 4)4 ] ⇒ ln = 2 ln(2 + 2) + 4 ln(4 + 4) ⇒

4

1

163

1

1 0

=2· 2

· 2 + 4 · 4

· 43 ⇒ 0 = 2

+ 4

⇒

+2

+4

+2

+4

4

163

0

2

2

4

4

+ 4

= ( + 2) ( + 4)

2 + 2

+4

ot

12

−1

⇒ ln = ln 4

+1

−1

4 + 1

1 0

1 1

1 1

=

−

· 43

2−1

2 4 + 1

65.

4

2

67.

1

2

1

1

ln( − 1) − ln(4 + 1) ⇒

2

2

−1

23

1

23

1

− 4

⇒ 0 =

− 4

⇒ 0 =

2( − 1)

+1

4 + 1 2 − 2

+1

⇒ ln =

N

63. =

Fo

61. = (2 + 2)2 (4 + 4)4

3

= 3

2

4

4

1

4

= 3 ln || = 3(ln 4 − ln 2) = 3 ln = 3 ln 2

2

2

2

1

1

1

1 5

1

= − ln |8 − 3| = − ln 2 − − ln 5 = (ln 5 − ln 2) = ln

8 − 3

3

3

3

3

3 2

1

Or: Let = 8 − 3. Then = −3 , so

2

2

2 1

− 3

1

1

1

1 5

1

=

= − ln || = − ln 2 − − ln 5 = (ln 5 − ln 2) = ln .

8 − 3

3

3

3

3

3 2

1

5

5

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

SECTION 6.2* THE NATURAL LOGARITHMIC FUNCTION

69.

1

= 1 2 + −

2

71. Let = ln . Then =

73.

¤

275

2 + + 1

1

+1+

=

= 1 2 + + ln 1 = 1 2 + + 1 − 1 + 1 + 0

2

2

2

1

1

2

⇒

(ln )2

=

2 =

1 3

1

+ = (ln )3 + .

3

3

sin 2 sin cos

= 2

= 2. Let = cos . Then = − sin , so

1 + cos2

1 + cos2

= −2 · 1 ln(1 + 2 ) + = − ln(1 + 2 ) + = − ln(1 + cos2 ) + .

2 = −2

2

1 + 2

Or: Let = 1 + cos2 .

75. (a)

1

(ln |sin | + ) = cos = cot

sin

√

77. The cross-sectional area is 1 + 1

1

0

2

= ( + 1). Therefore, the volume is

= [ln( + 1)]1 = (ln 2 − ln 1) = ln 2.

0

+1

79. =

2

1

=

1000

600

Fo

rS

al

e

(b) Let = 2 + 2 . Then = (2 + 2) = 2(1 + ) and ( + 1) = 1 , so

2

√

32

1 32

( + 1) 2 + 2 =

+ = 1 2 + 2

1 =

+ .

2

3

2 32

√

Or: Let = 2 + 2 . Then 2 = 2 + 2 ⇒ 2 = (2 + 2) ⇒ = (1 + ) , so

√

( + 1) 2 + 2 = · = 2 = 1 3 + = 1 (2 + 2 )32 + .

3

3

=

1000

600

1000

1

= ln | |

= (ln 1000 − ln 600) = ln 1000 = ln 5 .

600

3

600

ot

Initially, = , where = 150 kPa and = 600 cm3 , so = (150)(600) = 90,000. Thus,

= 90 000 ln 5 ≈ 45 974 kPa · cm3 = 45 974(103 Pa)(10−6 m3 ) = 45 974 Pa·m3 = 45 974 N·m [Pa = Nm2 ]

3

N

= 45 974 J

81. () = 2 + ln

⇒ 0 () = 2 + 1. If = −1 , then (1) = 2 ⇒ (2) = 1, so

0 (2) = 1 0 ((2)) = 1 0 (1) = 1 .

3

83. (a)

We interpret ln 15 as the area under the curve = 1 from = 1 to

= 15. The area of the rectangle is 1 · 2 = 1 . The area of the

2 3

3

1

1

2

5

trapezoid is 2 · 2 1 + 3 = 12 . Thus, by comparing areas, we observe that

1

3

ln 15

5

.

12

(b) With () = 1, = 10, and ∆ = 005, we have ln 15 =

15

(1) ≈ (005)[(1025) + (1075) + · · · + (1475)]

1

1

1

= (005) 1025 + 1075 + · · · + 1475 ≈ 04054

1

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

276

¤

CHAPTER 6 INVERSE FUNCTIONS

The area of is

85.

The area of is

1

1

1

1

and so + + · · · +

+1

2

3

1

1

1 and so 1 + + · · · +

2

−1

1

1

1

= ln .

1

= ln .

Note that if = 1, this has only the solution = 0, and no region is

al

more points. So we solve the equation (2 + 1) = ⇒ = 0 or

± −4()( − 1)

1

2

=±

− 1.

+ − 1 = 0 ⇒ = 0 or =

2

e

87. The curve and the line will determine a region when they intersect at two or

rS

determined. But if 1 − 1 0 ⇔ 1 1 ⇔ 0 1, then there are two solutions. [Another way of seeing this is to observe that the slope of the tangent to = (2 + 1) at the origin is 0 = 1 and therefore we must have 0 1.]

Note that we cannot just integrate between the positive and negative roots, since the curve and the line cross at the origin.

2

√1−1

√1−1

− = 2 1 ln(2 + 1) − 1 2 0

2

2

2 +1

1

1

= ln

−1+1 −

−1

− (ln 1 − 0)

1

+ − 1 = − ln − 1

= ln

N

ot

0

Fo

Since and (2 + 1) are both odd functions, the total area is twice the area between the curves on the interval

0 1 − 1 . So the total area enclosed is

89. If () = ln (1 + ), then 0 () =

Thus, lim

→0

1

, so 0 (0) = 1.

1+

ln(1 + )

()

() − (0)

= lim

= lim

= 0 (0) = 1.

→0

→0

−0

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

SECTION 6.3* THE NATURAL EXPONENTIAL FUNCTION

¤

277

6.3* The Natural Exponential Function

The function value at = 0 is 1 and the slope at = 0 is 1.

1.

⇔

⇔

(5)

10

(5)

= ln(10 ) = 10

(b) ln ln

1

1

=

52

25

7 − 4 = ln 6

(b) ln(3 − 10) = 2

7. (a) 3+1 =

(4)

= 5−2 =

⇔

7 − ln 6 = 4

3 − 10 = 2

⇔ 3 + 1 = ln

⇔

⇔

3 = 2 + 10

⇔ = 1 (ln − 1)

3

= 1 (7 − ln 6)

4

⇔

= 1 (2 + 10)

3

e

5. (a) 7−4 = 6

−2

al

3. (a) −2 ln 5 = ln 5

⇔ − 1 = −2

11. 2 − − 6 = 0

13. (a) 2+5 = 100

⇔ ln( − 1) = ln −2

⇔ −2 = ln( − 1) ⇔ = − 1 ln( − 1)

2

⇔ ( − 3)( + 2) = 0 ⇔ = 3 or −2 ⇒ = ln 3 since 0.

Fo

9. − −2 = 1

rS

(b) ln + ln( − 1) = ln(( − 1)) = 1 ⇔ ( − 1) = 1 ⇔ 2 − − = 0. The quadratic formula (with = 1,

√

= −1, and = −) gives = 1 1 ± 1 + 4 , but we reject the negative root since the natural logarithm is not

2

√ deﬁned for 0. So = 1 1 + 1 + 4 .

2

⇒ ln 2+5 = ln 100 ⇒ 2 + 5 = ln 100 ⇒ 5 = ln 100 − 2 ⇒

= 1 (ln 100 − 2) ≈ 05210

5

15. (a) ln 0

⇒ = 3 + 2 ⇒ = ln(3 + 2) ≈ 30949

ot

(b) ln( − 2) = 3 ⇒ − 2 = 3

⇒ 0

N

is 0 1.

⇒ 1. Since the domain of () = ln is 0, the solution of the original inequality

(b) 5 ⇒ ln ln 5 ⇒ ln 5

17.

=

= −

19. We start with the graph of = (Figure 2) and reﬂect about the -axis to get the graph of = − . Then we compress

the graph vertically by a factor of 2 to obtain the graph of = 1 − and then reﬂect about the -axis to get the graph of

2

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

278

¤

CHAPTER 6 INVERSE FUNCTIONS

= − 1 − . Finally, we shift the graph upward one unit to get the graph of = 1 − 1 − .

2

2

√

3 − 2 , we must have 3 − 2 ≥ 0 ⇒ 2 ≤ 3

21. (a) For () =

⇒

2 ≤ ln 3 ⇒ ≤

1

2

ln 3.

Thus, the domain of is (−∞ 1 ln 3].

2

(b) = () =

√

3 − 2

[note that ≥ 0] ⇒ 2 = 3 − 2

⇒ 2 = ln(3 − 2 ) ⇒

ln(3 − 2 ). So −1 () = 1 ln(3 − 2 ). For the domain of −1 ,

2

√

√

√

√

2

2

we must have 3 − 0 ⇒ 3 ⇒ || 3 ⇒ − 3 3 ⇒ 0 ≤ 3 since ≥ 0. Note

√

that the domain of −1 , [0 3 ), equals the range of .

1

2

1

2

⇒ = ln(+3) = + 3 ⇒ = − 3.

23. = ln( + 3)

25. = () =

3

⇒ ln = 3

⇒ =

rS

Interchange and : the inverse function is = − 3.

al

e

=

ln(3 − 2 ). Interchange and : =

⇒ 2 = 3 − 2

√

√

√

3

ln . Interchange and : = 3 ln . So −1 () = 3 ln .

3 − −3

1 − −6

1−0

=1

= lim

=

→∞ 1 + −6

3 + −3

1+0

Fo

27. Divide numerator and denominator by 3 : lim

→∞

29. Let = 3(2 − ). As → 2+ , → −∞. So lim 3(2−) = lim = 0 by (6).

→2+

→−∞

31. Since −1 ≤ cos ≤ 1 and −2 0, we have −−2 ≤ −2 cos ≤ −2 . We know that lim (−−2 ) = 0 and

ot

→∞

lim −2 = 0, so by the Squeeze Theorem, lim (−2 cos ) = 0.

→∞

→∞

N

33. () = 5 is a constant function, so its derivative is 0, that is, 0 () = 0.

35. By the Product Rule, () = (3 + 2)

⇒

0 () = (3 + 2)( )0 + (3 + 2)0 = (3 + 2) + (32 + 2)

= [(3 + 2) + (32 + 2)] = (3 + 32 + 2 + 2)

37. By (9), =

39. = −

41. () = 1

3

⇒ 0 =

3

3

(3 ) = 32 .

⇒ 0 = − (−) + − · 1 = − (− + 1) or (1 − )−

⇒ 0 () = 1 ·

43. By (9), () = sin 2

1

−1

−1

= 1

=

1

2

2

⇒ 0 () = sin 2 ( sin 2)0 = sin 2 ( · 2 cos 2 + sin 2 · 1) = sin 2 (2 cos 2 + sin 2)

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

SECTION 6.3* THE NATURAL EXPONENTIAL FUNCTION

45. =

√

1 + 23

47. =

49. By the Quotient Rule, =

0 =

279

1

1

33

(1 + 23 )−12

(1 + 23 ) = √

(23 · 3) = √

3

2

2 1 + 2

1 + 23

⇒ 0 =

⇒ 0 = ·

¤

( ) = · or +

+

+

⇒

( + )( ) − ( + )( )

( + − − )

( − )

=

=

.

+ )2

+ )2

(

(

( + )2

51. = cos

1 − 2

1 + 2

⇒

53. = 2 cos

al

e

1 − 2

1 − 2

(1 + 2 )(−22 ) − (1 − 2 )(22 )

1 − 2

·

= − sin

·

0 = − sin

2

2

2

1+

1 +

1+

(1 + 2 )2

−22 (1 + 2 ) + (1 − 2 )

1 − 2

1 − 2

1 − 2

42

−22 (2)

= − sin

= − sin

=

· sin

·

·

1 + 2

(1 + 2 )2

1 + 2

(1 + 2 )2

(1 + 2 )2

1 + 2

⇒ 0 = 2 (− sin ) + (cos )(22 ) = 2 (2 cos − sin ).

( ) =

( − ) ⇒ ·

·

· 1 − · 0

= 1 − 0

2

·

⇒

0

1

−

· = 1 − 0

2

⇒

0 −

0

· =1−

2

⇒

−

( − )

⇒ 0 = 2

= 2

−

−

2

ot

−

0 1 −

=

2

⇒

= 1 − 0

Fo

55.

rS

At (0 1), 0 = 1(2 − 0) = 2, so an equation of the tangent line is − 1 = 2( − 0), or = 2 + 1.

⇒ 0 = − 1 −2 ⇒ 00 = + 1 −2 , so

2

4

200 − 0 − = 2 + 1 −2 − − 1 −2 − + −2 = 0.

4

2

N

57. = + −2

59. =

⇒ 0 =

⇒

00 = 2 , so if = satisﬁes the differential equation 00 + 6 0 + 8 = 0,

then 2 + 6 + 8 = 0; that is, (2 + 6 + 8) = 0. Since 0 for all , we must have 2 + 6 + 8 = 0, or ( + 2)( + 4) = 0, so = −2 or −4.

61. () = 2

⇒ 0 () = 22

000 () = 22 · 22 = 23 2

⇒ 00 () = 2 · 22 = 22 2

⇒ ···

⇒

⇒ () () = 2 2

63. (a) () = + is continuous on R and (−1) = −1 − 1 0 1 = (0), so by the Intermediate Value Theorem,

+ = 0 has a root in (−1 0).

(b) () = + ⇒ 0 () = + 1, so +1 = −

+

. Using 1 = −05, we get 2 ≈ −0566311,

+ 1

3 ≈ −0567143 ≈ 4 , so the root is −0567143 to six decimal places. c ° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

280

¤

CHAPTER 6 INVERSE FUNCTIONS

65. (a) lim () = lim

→∞

→∞

1

1

= 1, since 0 ⇒ − → −∞ ⇒ − → 0.

=

1 + −

1+·0

(b) () = (1 + − )−1

⇒

−

= −(1 + − )−2 (−− ) =

(1 + − )2

(c)

From the graph of () = (1 + 10−05 )−1 , it seems that () = 08

(indicating that 80% of the population has heard the rumor) when

≈ 74 hours.

67. () = −

⇒ 0 () = 1 − = 0 ⇔ = 1 ⇔ = 0. Now 0 () 0 for all 0 and 0 () 0 for all

0, so the absolute maximum value is (0) = 0 − 1 = −1.

, [−1 4]. 0 () = · −

2 8

· (− ) + −

4

2 8

2 8

· 1 = −

2 8

2

(− + 1). Since −

4

e

2 8

69. () = −

is never 0,

() = 0 ⇒ − 4 + 1 = 0 ⇒ 1 = 4 ⇒ = 4 ⇒ = ±2, but −2 is not in the given interval, [−1 4].

√

(−1) = −−18 ≈ −088, (2) = 2−12 ≈ 121, and (4) = 4−2 ≈ 054. So (2) = 2−12 = 2 is the absolute

√

maximum value and (−1) = −−18 = −1 8 is the absolute minimum value.

0

2

2

71. (a) () = (1 − )−

rS

al

2

⇒ 0 () = (1 − )(−− ) + − (−1) = − ( − 2) 0 ⇒ 2, so is increasing on

(2 ∞) and decreasing on (−∞ 2).

Fo

(b) 00 () = − (1) + ( − 2)(−− ) = − (3 − ) 0 ⇔ 3, so is CU on (−∞ 3) and CD on (3 ∞).

(c) 00 changes sign at = 3, so there is an IP at 3 −2−3 .

73. = () = −1(+1)

→±∞

lim −1(+1) = ∞ since −1( + 1) → ∞, so = −1 is a VA.

E. 0 () = −1(+1) ( + 1)2

⇒ 0 () 0 for all except 1, so

is increasing on (−∞ −1) and (−1 ∞). F. No extreme values

G. 00 () =

lim −1(+1) = 0 since

→−1+

→−1−

N

−1 ( + 1) → −∞,

lim −1(+1) = 1 since −1( + 1) → 0, so = 1 is a HA.

ot

C. No symmetry D.

A. = { | 6= −1} = (−∞ −1) ∪ (−1, ∞) B. No -intercept; -intercept = (0) = −1

H.

−1(+1)

−1(+1) (−2)

−1(+1) (2 + 1)

+

=−

( + 1)4

( + 1)3

( + 1)4

⇒

00 () 0 ⇔ 2 + 1 0 ⇔ − 1 , so is CU on (−∞ −1)

2

1

1 and −1 − 2 , and CD on − 2 , ∞ . has an IP at − 1 , −2 .

2

75. = 1(1 + − )

A. = R B. No -intercept; -intercept = (0) = 1 C. No symmetry

2

D. lim 1(1 + − ) =

→∞

1

1+0

= 1 and lim 1(1 + − ) = 0 since lim − = ∞, so has horizontal asymptotes

0

→−∞

− −2

= 0 and = 1. E. () = −(1 +

F. No extreme values G. 00 () =

)

→−∞

−

(−

−

)=

− 2

(1 +

) . This is positive for all , so is increasing on R.

(1 + − )2 (−− ) − − (2)(1 + − )(−− )

− (− − 1)

=

− )4

(1 +

(1 + − )3

c

° 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.

SECTION 6.3* THE NATURAL EXPONENTIAL FUNCTION

The second factor in the numerator is negative for 0 and positive for 0,

¤

281

H.

and the other factors are always positive, so is CU on (−∞, 0) and CD

on (0 ∞). IP at 0, 1

2

77. () = − with = 001, = 4, and = 007. We will ﬁnd the

zeros of 00 for () = − .

0 () = (−− ) + − (−1 ) = − (− + −1 )

00 () = − (−−1 + ( − 1)−2 ) + (− + −1 )(−− )

= −2 − [− + ( − 1) + 2 2 − ]

e

= −2 − (2 2 − 2 + 2 − )

Using the given values of and gives us 00 () = 2 −007 (000492 − 056 + 12). So