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: 25

Answer

$y=\sqrt 5x^3\ln x-x^3-Cx^{-2}$

Work Step by Step

We are given: $$\frac{dy}{dx}+\frac{1}{x}y=\frac{25x^2 \ln x}{2y}$$ Multiplying both sides by $y$ $$y\frac{dy}{dx}+\frac{1}{x}y^2=\frac{25x^2 \ln x}{2}$$ Assume $u=y^2 \rightarrow \frac{du}{dx}=2y \frac{dy}{dx}$ The equation becomes: $$\frac{1}{2}\frac{du}{dx}+\frac{1}{x}du=\frac{25x^2 \ln x}{2}$$ $$\frac{du}{dx}+\frac{2}{x}u=25x^2 \ln x$$ Integrating factor: $$I=e^{\int \frac{2}{x} dx}=e^{2\ln x dx}=x^2$$ The equation becomes: $$\frac{d}{dx}(ux^2)=25x^4\ln x$$ Integrating both sides: $$ux^2=25(\frac{1}{5}x^5\ln x-\frac{1}{25}x^5)+C$$ $$u=5x^3\ln x-x^3-Cx^{-2}$$ Since $u=y^2$ $$y^2=5x^3\ln x-x^3-Cx^{-2}$$ Hence general solution is $y=\sqrt 5x^3\ln x-x^3-Cx^{-2}$
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.