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: 6

Answer

\[\frac{3}{11(2x-1)}+\frac{89}{33(x+5)}+\frac{-4}{3(x+2)}\]

Work Step by Step

In this case the general form of the partial fraction decomposition is \[\frac{3x^2-2x+14}{(2x-1)(x +5)(x+2)}=\frac{A}{2x-1}+\frac{B}{x+5}+\frac{C}{x+2}\;\;\;...(*)\] \[\Rightarrow 3x^2-2x+4=A(x+5)(x+2)+B(2x-1)(x+2)+C(2x-1)(x+5) \;\;\;...(1)\] Put $x=\frac{1}{2}$ in (1) \[\frac{3}{4}-1+4=A\left(\frac{11}{2}\right)\left(\frac{5}{2}\right)\] \[\frac{15}{4}=\frac{55A}{4}\] \[\Rightarrow A=\frac{3}{11}\] Put $x=-5$ in (1) \[3(25)+10+4=B(-11)(-3)\] \[\Rightarrow 89=33B\] \[\Rightarrow B=\frac{89}{33}\] Put $x=-2$ in (1) \[12+4+4=C(-5)(3)\] \[20=C(-15)\] \[C=\frac{-4}{3}\] From (*) \[\frac{3x^2-2x+14}{(2x-1)(x +5)(x+2)}=\frac{3}{11(2x-1)}+\frac{89}{33(x+5)}+\frac{-4}{3(x+2)}\] Hence, \[\frac{3x^2-2x+14}{(2x-1)(x +5)(x+2)}=\frac{3}{11(2x-1)}+\frac{89}{33(x+5)}+\frac{-4}{3(x+2)}.\]
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