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: 10

Answer

\[\frac{3x-2}{(x-5)(x^2+1)}=\frac{1}{2(x-5)}-\frac{x-1}{2(x^2+1)}\]

Work Step by Step

In this case the general form of the partial fraction decomposition is \[\frac{3x-2}{(x-5)(x^2+1)}=\frac{A}{x-5}+\frac{Bx+C}{x^2+1}\;\;\;...(*)\] \[3x-2=A(x^2+1)+(Bx+C)(x-5)\] \[3x-2=A(x^2+1)+(Bx^2-5Bx+Cx-5C)\] \[3x-2=(A+B)x^2+(C-5B)x+(A-5C)\] Comparing like coefficients \[C-5B=3\;\;\;...(1)\] \[A-5C=-2\;\;\; ...(2)\] \[A+B=0\Rightarrow B=-A\;\;\;...(3)\] Using (3) in (1) then (1) becomes \[C+5A=3\;\;\;...(4)\] Multiply (4) by 5 then add to (1) \[26A=13\Rightarrow A=\frac{1}{2}\] From (3) \[B=\frac{-1}{2}\] From (1) \[C=3+5B\Rightarrow C=3-\frac{5}{2}\] \[\Rightarrow C=\frac{1}{2}\] From (*) \[\frac{3x-2}{(x-5)(x^2+1)}=\frac{1}{2(x-5)}+\frac{\frac{-1}{2}x+\frac{1}{2}}{x^2+1}\] \[\frac{3x-2}{(x-5)(x^2+1)}=\frac{1}{2(x-5)}-\frac{x-1}{2(x^2+1)}\] Hence,\[\frac{3x-2}{(x-5)(x^2+1)}=\frac{1}{2(x-5)}-\frac{x-1}{2(x^2+1)}.\]
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