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: 4

Answer

\[\frac{4}{x+3}+\frac{1}{3(x-1)}-\frac{10}{3(x+2)}\]

Work Step by Step

In this case the general form of the partial fraction decomposition is \[\frac{x^2-x+4}{(x + 3)(x - 1)(x+2)}=\frac{A}{x+3}+\frac{B}{x-1}+\frac{C}{x+2}\;\;\;...(*)\] \[\Rightarrow x^2-x+4=A(x-1)(x+2)+B(x+3)(x+2)+C(x+3)(x-1) \;\;\;...(1)\] Put $x=-3$ in (1) \[9+3+4=A(-4)(-1)\] \[\Rightarrow 16=4A\Rightarrow A=4\] Put $x=1$ in (1) \[1-1+4=B(4)(3)\] \[\Rightarrow B=\frac{4}{12}=\frac{1}{3}\] Put $x=-2 $ in (1) \[4+2+4=C(1)(-3)\] \[\Rightarrow C=\frac{-10}{3}\] From (*) \[\frac{x^2-x+4}{(x + 3)(x - 1)(x+2)}=\frac{4}{x+3}+\frac{1}{3(x-1)}+\frac{-10}{3(x+2)}\] Hence ,\[\frac{x^2-x+4}{(x + 3)(x - 1)(x+2)}=\frac{4}{x+3}+\frac{1}{3(x-1)}+\frac{-10}{3(x+2)}.\]
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