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: 5

Answer

\[\frac{-1}{2(x+4)}+\frac{1}{6(x-2)}+\frac{1}{3(x+1)}\]

Work Step by Step

In this case the general form of the partial fraction decomposition is \[\frac{2x-1}{(x + 4)(x - 2)(x+1)}=\frac{A}{x+4}+\frac{B}{x-2}+\frac{C}{x+1}\;\;\;...(*)\] \[\Rightarrow 2x-1=A(x-2)(x+1)+B(x+4)(x+1)+C(x+4)(x-2) \;\;\;...(1)\] Put $x=-4$ in (1) \[-9=A(-6)(-3)\Rightarrow A=\frac{-9}{18}\] \[\Rightarrow A=\frac{-1}{2}\] Put $x=2$ in (1) \[4-1=3=B(6)(3)\Rightarrow B=\frac{1}{6}\] Put $x=-1$ in (1) \[-3=C(3)(-3)\Rightarrow C=\frac{1}{3}\] From (*) \[\frac{2x-1}{(x + 4)(x - 2)(x+1)}=\frac{-1}{2(x+4)}+\frac{1}{6(x-2)}+\frac{1}{3(x+1)}\] Hence , \[\frac{2x-1}{(x + 4)(x - 2)(x+1)}=\frac{-1}{2(x+4)}+\frac{1}{6(x-2)}+\frac{1}{3(x+1)}.\]
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