Calculus 8th Edition

Published by Cengage
ISBN 10: 1285740629
ISBN 13: 978-1-28574-062-1

Chapter 9 - Differential Equations - 9.5 Linear Equations - 9.5 Exercises - Page 665: 19

Answer

$$ y=-x\cos x- x$$

Work Step by Step

Given $$x y^{\prime}=y+x^{2} \sin x, \quad y(\pi)=0$$ Rewriting the equation as $$ y^{\prime}-\frac{1}{x} y=x\sin x $$ Since the equation is linear and $p(x)= \frac{-1}{x} $ and $q(x)=x\sin x $, then \begin{align*} \mu &=e^{\int p(x)}dx\\ &= e^{\int \frac{-1}{x} dx}\\ &=e^{-\ln x}\\ &=x^{-1} \end{align*} Hence the general solution given by \begin{align*} \mu(x)y&=\int \mu(x)q(x)dx\\ x^{-1} y&= \int x^{-1} x\sin x dx\ \ \\ &=\int \sin xdx\\ &= -\cos x+C \end{align*} Then $$ y=-x\cos x+Cx$$ Since $y(\pi )=0 $, then $C=-1$, hence $$ y=-x\cos x- x$$
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