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 - 1.8 Change of Variables - Problems - Page 79: 10

Answer

$y=ce^{-\frac{3}{2}\frac{x}{y}}$

Work Step by Step

Given: $$(3x-2y)\frac{dy}{dx}=3y$$ Let $y=vx \rightarrow \frac{dy}{dx}=v+x\frac{dv}{dx}$ Subtituting: $$(3-2v)(v+x\frac{dv}{dx})=3v$$ $$x\frac{dv}{dx}=\frac{3v}{3-2v}-v$$ $$x\frac{dv}{dx}=\frac{3v-3v+2v^2}{3-2v}$$ $$x\frac{dv}{dx}=\frac{2v^2}{3-2v}$$ $$\frac{3-2v}{2v^2}dv=\frac{dx}{x}$$ Integrating left side: $$\int \frac{3-2v}{2v^2}=\int \frac{dx}{x}+C$$ $$-\frac{3}{2}v^{-1}-\ln v=\ln|X| + C$$ where $c$ is a constant of integration. $$\ln x + \ln v=-c-\frac{3}{2}v$$ $$\ln (xv)=-c-\frac{3}{2}v$$ Subtitute when $y=vx \rightarrow \ln y=-c-\frac{3}{2}\frac{x}{y}$ Solve for $y$ $$y=ce^{-\frac{3}{2}\frac{x}{y}}$$
Update this answer!

You can help us out by revising, improving and updating this answer.

Update this answer

After you claim an answer you’ll have 24 hours to send in a draft. An editor will review the submission and either publish your submission or provide feedback.