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: 2

Answer

\[\frac{x-2}{(x - 1)(x + 4)}=\frac{-1}{5(x-1)}+\frac{6}{5(x+4)}\]

Work Step by Step

The general form of the decomposition is \[\frac{x-2}{(x - 1)(x + 4)}=\frac{A}{x-1}+\frac{B}{x+4}\;\;\;...(*)\] \[\Rightarrow (x-2)=A(x+4)+B(x-1)\] \[\Rightarrow x-2=(A+B)x+(4A-B)\] Comparing like coefficients $A+B=1\;\;\;...(1)$ $4A-B=-2\;\;\;...(2)$ Adding equation (1) and (2) $5A=-1\Rightarrow A=\frac{-1}{5}$ From (1) $\Rightarrow B=\frac{6}{5}$ From (*) \[\frac{x-2}{(x - 1)(x + 4)}=\frac{-1}{5(x-1)}+\frac{6}{5(x+4)}\] Hence, $\frac{x-2}{(x - 1)(x + 4)}=\frac{-1}{5(x-1)}+\frac{6}{5(x+4)}$.
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