Differential Equations and Linear Algebra (4th Edition)

Published by Pearson
ISBN 10: 0-32196-467-5
ISBN 13: 978-0-32196-467-0

Chapter 1 - First-Order Differential Equations - 1.12 Chapter Review - Additional Problems - Page 110: 29

Answer

$y=xe^{Cx}$

Work Step by Step

We are given: $$y[\ln(\frac{y}{x}+1]dx-xdy=0$$ Rewrite as: $$\frac{dy}{dx}=\frac{y}{x}(\ln\frac{y}{x}+1)$$ Assume that $V=\frac{y}{x} \rightarrow \frac{dy}{dx}=V+x\frac{dV}{dy}$ The equation becomes: $$V+ x\frac{dV}{dx}=V(\ln V+1)$$ $$ x\frac{dV}{dx}=V\ln V$$ $$\frac{1}{V\ln V}dV=\frac{1}{x}dx$$ Integrating both sides: $$\ln(\ln V)=\ln |xC|$$ $$V=e^{Cx}$$ $$\frac{y}{x}=e^{Cx}$$ Hence general solution is $y=xe^{Cx}$
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