Differential Equations and Linear Algebra (4th Edition)

Published by Pearson
ISBN 10: 0-32196-467-5
ISBN 13: 978-0-32196-467-0

Appendix C - Review of Integration Techniques - Exercises for C - Problems - Page 810: 8

Answer

\[I=\frac{3}{4}\ln |x-1|+\frac{1}{4}\ln |x+3|+C\] Where $C$ is constant of integration

Work Step by Step

Let \[I=\int\frac{x+2}{(x-1)(x+3)}dx\] \[\frac{x+2}{(x-1)(x+3)}=\frac{A}{x-1}+\frac{B}{x+3}\;\;\;...(*)\] \[x+2=A(x+3)+B(x-1)\] \[x+2=(A+B)x+(3A-B)\] Comparing coefficients both side \[A+B=1\;\;\;...(1)\] \[3A-B=2\;\;\;...(2)\] Add equation (1) and (2) \[4A=3\Rightarrow A=\frac{3}{4}\] From (1) \[B=\frac{1}{4}\] From (*) \[\frac{x+2}{(x-1)(x+3)}=\frac{3}{4(x-1)}+\frac{1}{4(x+3)}\] \[\Rightarrow I=\int\left[\frac{3}{4(x-1)}+\frac{1}{4(x+3)}\right]dx\] \[\Rightarrow I=\frac{3}{4}\ln |x-1|+\frac{1}{4}\ln |x+3|+C\] Where $C$ is constant of integration Hence , \[I=\frac{3}{4}\ln |x-1|+\frac{1}{4}\ln |x+3|+C\;.\]
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