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 - 1.6 First-Order Linear Differential Equations - Problems - Page 59: 15

Answer

\[y(x)=\frac{x}{m+1}\ln x-\frac{x}{(m+1)^2}+\frac{C}{x^m}\]

Work Step by Step

$y'+mx^{-1}y=\ln x$ ____(1) (1) is Linear Differential Equation Integrating Factor:- \[I(x)=e^{\int mx^{-1} dx}=e^{m\int\frac{1}{x} dx}=e^{m\ln x}=x^m\] Multiply (1) by $I(x)$ \[x^m\frac{dy}{dx}+mx^{m-1}y=x^m \ln x\] \[\frac{d}{dx}(yx^m)=x^m\ln x\] Integrating \[yx^m=\int x^m\ln x dx+C\] $C$ is constant of integration \[yx^m=\ln x\left(\frac{x^{m+1}}{m+1}\right)-\int\frac{1}{x}\left(\frac{x^{m+1}}{m+1}\right)dx+C\] \[yx^m=\ln x\left(\frac{x^{m+1}}{m+1}\right)-\frac{x^{m+1}}{(m+1)^2}+C\] \[y(x)=\ln x\left(\frac{x}{m+1}\right)-\frac{x}{(m+1)^2}+\frac{C}{x^m}\] Hence General Solution of (1) is $y(x)=\frac{x}{m+1}\ln x-\frac{x}{(m+1)^2}+\frac{C}{x^m}$.
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