Differential Equations and Linear Algebra (4th Edition)

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

Appendix B - Review of Partial Fractions - Exercises for B - Problems - Page 803: 13

Answer

\[\frac{7x+2}{(x-2)(x+2)^2}=\frac{1}{(x-2)}-\frac{1}{x+2}+\frac{3}{(x+2)^2}\]

Work Step by Step

In this case the general form of the partial fraction decomposition is \[\frac{7x+2}{(x-2)(x+2)^2}=\frac{A}{(x-2)}+\frac{B}{x+2}+\frac{C}{(x+2)^2}\;\;\;...(*)\] \[7x+2=A(x+2)^2+B(x-2)(x+2)+C(x-2)\] \[7x+2=A(x^2+4+4x)+B(x^2-4)+C(x-2)\] \[7x+2=(A+B)x^2+(4A+C)x+(4A-4B-2C)\] Comparing like coefficients \[A+B=0\Rightarrow B=-A\;\;\;...(1)\] \[4A+C=7\;\;\;...(2)\] \[4A-4B-2C=2\;\;\;...(3)\] Using (1) in (3) then (3) becomes \[8A-2C=2\;\;\;...(4)\] Multiply (2) by 2 then add to (4) \[16A=16\Rightarrow A=1\] From (1) \[B=-1\] From (2) \[C=3\] From (*) \[\frac{7x+2}{(x-2)(x+2)^2}=\frac{1}{(x-2)}+\frac{-1}{x+2}+\frac{3}{(x+2)^2}\] Hence, \[\frac{7x+2}{(x-2)(x+2)^2}=\frac{1}{(x-2)}-\frac{1}{x+2}+\frac{3}{(x+2)^2}.\]
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