Calculus 8th Edition

Published by Cengage
ISBN 10: 1285740629
ISBN 13: 978-1-28574-062-1

Chapter 7 - Techniques of Integration - 7.8 Improper Integrals - 7.8 Exercises - Page 574: 30

Answer

Divergent

Work Step by Step

Let \[I=\int_{-1}^{2}\frac{x}{(x+1)^2}dx\] Since $-1$ is point of infinite discontinuity of integrand $\large\frac{x}{(x+1)^2}$ \[I=\lim_{t\rightarrow -1^+}\int_{t}^{2}\frac{x}{(x+1)^2}dx\;\;\;\ldots (1)\] Let \[I_1=\int\frac{x}{(x+1)^2}dx\] Substitute $\; r=x+1\;\;\;\ldots (2)$ \[\Rightarrow dr=dx\] \[I_1=\int\frac{r-1}{r^2}dr\] \[I=\int\left(\frac{1}{r}-r^{-2}\right)dr\] \[I=\ln r-\frac{r^{-1}}{-1}=\ln r+\frac{1}{r}\] From (2) \[I_1=\ln (x+1)+\frac{1}{(x+1)}\;\;\;\ldots (3)\] Using (3) in (1) \[I=\lim_{t\rightarrow -1^+}\left[\ln (x+1)+\frac{1}{(x+1)}\right]_{t}^{2}\] \[I=\lim_{t\rightarrow -1^+}\left[\ln 3+\frac{1}{3}-\ln (t+1)-\frac{1}{(t+1)}\right]\] $\;\;\;\;\;\;\;\;\;\;\;\;= $ does not exist Since limit on R.H.S. of (1) does not exists so $I$ is divergent.
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