Calculus: Early Transcendentals 8th Edition

Published by Cengage Learning
ISBN 10: 1285741552
ISBN 13: 978-1-28574-155-0

Chapter 9 - Review - Exercises - Page 635: 5

Answer

The solution of the differential equation $$ y^{\prime}=x e^{-\sin x}-y \cos x $$ is $$ y=\left(\frac{1}{2} x^{2}+C\right) e^{-\sin x} $$ where $ C $ is an arbitrary constant

Work Step by Step

$$ y^{\prime}=x e^{-\sin x}-y \cos x $$ $$ \Rightarrow \quad y^{\prime}+(\cos x) y=x e^{-\sin x} \quad\quad (1) $$ This is a linear equation and the integrating factor is $$ I(x)=e^{\int \cos x d x}=e^{\sin x} $$ Multiplying Eq.(1) by $e^{\sin x}$ gives $$ e^{\sin x} y^{\prime}+e^{\sin x}(\cos x) y=x .\quad\left(e^{\sin x} y\right)^{\prime}=x $$ When we integrate both sides of the last equation we get: $$ e^{\sin x} y=\frac{1}{2} x^{2}+C \Rightarrow y=\left(\frac{1}{2} x^{2}+C\right) e^{-\sin x} $$ So the solution of the differential equation $$ y^{\prime}=x e^{-\sin x}-y \cos x $$ is $$ y=\left(\frac{1}{2} x^{2}+C\right) e^{-\sin x} $$ where $ C $ is an arbitrary constant
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