Calculus: Early Transcendentals 9th Edition

Published by Cengage Learning
ISBN 10: 1337613924
ISBN 13: 978-1-33761-392-7

Chapter 7 - Section 7.1 - Integration by Parts - 7.1 Exercises - Page 491: 66

Answer

$A \approx 1.6925$

Work Step by Step

$$\eqalign{ & {\text{Let }}y = x\ln \left( {x + 1} \right){\text{ and }}y = 3x - {x^2} \cr & {\text{From the graph we have the intersection points}} \cr & x = 0{\text{ and }}x \approx 1.93 \cr & {\text{The area of the region bounded by the curves is given by:}} \cr & A = \int_0^{1.93} {\left[ {\left( {3x - {x^2}} \right) - x\ln \left( {x + 1} \right)} \right]} dx \cr & \cr & {\text{* Integrating }}\int {x\ln \left( {x + 1} \right)} dx \cr & u = \ln \left( {x + 1} \right),{\text{ }}du = \frac{1}{{x + 1}}dx \cr & dv = xdx,{\text{ }}v = \frac{{{x^2}}}{2} \cr & = \frac{{{x^2}}}{2}\ln \left( {x + 1} \right) - \underbrace {\frac{1}{2}\int {\frac{{{x^2}}}{{x + 1}}} dx}_{{\text{Use the long division}}} \cr & = \frac{{{x^2}}}{2}\ln \left( {x + 1} \right) - \frac{1}{2}\int {\left( {x - 1 + \frac{1}{{x + 1}}} \right)} dx \cr & = \frac{{{x^2}}}{2}\ln \left( {x + 1} \right) - \frac{1}{2}\left( {\frac{{{x^2}}}{2} - x + \ln \left| {x + 1} \right|} \right) + C \cr & = \frac{{{x^2}}}{2}\ln \left( {x + 1} \right) - \frac{{{x^2}}}{4} + \frac{1}{2}x - \frac{1}{2}\ln \left| {x + 1} \right| + C \cr & \cr & {\text{Therefore}}{\text{,}} \cr & \underbrace {A \approx \int_0^{1.93} {\left[ {\left( {3x - {x^2}} \right) - x\ln \left( {x + 1} \right)} \right]} dx}_ \Downarrow \cr & A \approx \left[ {\frac{3}{2}{x^2} - \frac{1}{3}{x^3} - \frac{{{x^2}}}{2}\ln \left( {x + 1} \right) + \frac{{{x^2}}}{4} - \frac{1}{2}x + \frac{1}{2}\ln \left| {x + 1} \right|} \right]_0^{1.93} \cr & {\text{Evaluating the limits we obtain}} \cr & A \approx \left[ {1.6925} \right] - \left[ 0 \right] \cr & A \approx 1.6925 \cr} $$
Update this answer!

You can help us out by revising, improving and updating this answer.

Update this answer

After you claim an answer you’ll have 24 hours to send in a draft. An editor will review the submission and either publish your submission or provide feedback.