Differential Equations and Linear Algebra (4th Edition)

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

Chapter 8 - Linear Differential Equations of Order n - 8.8 A Differential Equation with Nonconstant Coefficients - Problems - Page 568: 20

Answer

See below

Work Step by Step

Given $x^2y''-3xy'+4y=\frac{x^2}{\ln x}$ In this case the substitution $y(x) = x^r$ yields the indicial equation $$r(r-1)-3r+4=0\\ r^2-4r+4=0$$ It follows that two linearly independent solutions to the given differential equation are $u_1(x)=x^{2}\\ u_2(x)=x^{2}\ln x$ so that the general solution is $y(x)=u_1(x)x^{2}+u_2(x)x^{2}\ln x$ where $u_1$ and $u_2$ are determined from $u_1'(x)x^{2}+u_2'(x)x^{2}\ln x=0\\ u_1'(x)(x^{2})'+u'_2(x)(x^{2}\ln x)'=\frac{x^2}{\ln x}$ Hence, $u_1'=-\frac{1}{2x(\ln x-1)}\\ u_2'=\frac{1}{2\ln x x(\ln x-1)}$ which upon integration gives $u_1(x)=-\frac{1}{2}\ln (\ln x-1)\\ u_2(x)=\frac{1}{2}\ln (\ln x-1)$ Thus, the given equation has general solution $y(x)=c_1x^{2}+c_2x^{2}\ln x-\frac{1}{2}x^2\ln (\ln x-1)+\frac{1}{2}x^2\ln (\frac{\ln x-1}{\ln x})\ln x$
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