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: 21

Answer

$y(x)=c_1x^{m}+c_2x^{m}\ln x+\frac{x^m(\ln x)^{k+1}}{(k+1)(k+2)}$

Work Step by Step

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