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: 13

Answer

\[I=2\ln |x|-2\ln |x+1|-\frac{1}{x+1}+C\] Where $C$ is constant of integration

Work Step by Step

Let \[I=\int\frac{3x+2}{x(x+1)^2}dx\] We first determine the partial fraction decomposition of the integrand \[\frac{3x+2}{x(x+1)^2}=\frac{A}{x}+\frac{B}{x+1}+\frac{C}{(x+1)^2}\;\;\;...(*)\] \[3x+2=A(x+1)^2+Bx(x+1)+Cx\] \[3x+2=A(x^2+2x+1)+Bx^2+Bx+Cx\] \[3x+2=(A+B)x^2+(2A+B+C)x+A\] Comparing like coefficients both side \[A+B=0\Rightarrow B=-A\;\;\;...(1)\] \[2A+B+C=3\;\;\;...(2)\] \[A=2\] From (1) \[B=-2\] From (2) \[C=1\] From (*) \[\frac{3x+2}{x(x+1)^2}=\frac{2}{x}-\frac{2}{x+1}+\frac{1}{(x+1)^2}\] \[\Rightarrow I=\int\left[\frac{2}{x}-\frac{2}{x+1}+\frac{1}{(x+1)^2}\right]dx\] \[\Rightarrow I=2\ln |x|-2\ln |x+1|-\frac{1}{x+1}+C\] Where $C$ is constant of integration Hence , \[I=2\ln |x|-2\ln |x+1|-\frac{1}{x+1}+C\:.\]
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