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: 11

Answer

\[\frac{x^2+6}{(x-2)(x^2+16)}=\frac{1}{2(x-2)}+\frac{x+2}{2(x^2+16)}\]

Work Step by Step

In this case the general form of the partial fraction decomposition is \[\frac{x^2+6}{(x-2)(x^2+16)}=\frac{A}{x-2}+\frac{Bx+C}{x^2+16}\;\;\;...(*)\] \[x^2+6=A(x^2+16)+(Bx+C)(x-2)\] \[x^2+6=A(x^2+16)+(Bx^2-2Bx+Cx-2C)\] \[x^2+6=(A+B)x^2+(C-2B)x+(16A-2C)\] Comparing like coefficients \[A+B=1\;\;\;...(1)\] \[C-2B=0\Rightarrow C=2B\;\;\;...(2)\] \[16A-2C=6\:\;\;...(3)\] Using (2) in (3) then (3) becomes \[16A-4B=6\;\:\;...(4)\] Multiply (1) by 4 then add to (4) \[20A=10\Rightarrow A=\frac{1}{2}\] From (1) \[B=\frac{1}{2}\] From (2) \[C=1\] From (*) \[\frac{x^2+6}{(x-2)(x^2+16)}=\frac{1}{2(x-2)}+\frac{\frac{1}{2}x+1}{x^2+16}\] \[\frac{x^2+6}{(x-2)(x^2+16)}=\frac{1}{2(x-2)}+\frac{x+2}{2(x^2+16)}\] Hence , \[\frac{x^2+6}{(x-2)(x^2+16)}=\frac{1}{2(x-2)}+\frac{x+2}{2(x^2+16)}.\]
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