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 567: 18

Answer

$y(x)=c_1x^2+c_2x^3-x^2\sin x$

Work Step by Step

Given $x^2y''-4xy'+6y=x^4\sin x$ In this case the substitution $y(x) = x^r$ yields the indicial equation $$r(r-1)-4r+6=0\\ r^2-5r+6=0$$ It follows that two linearly independent solutions to the given differential equation are $u_1(x)=x^2\\ u_2(x)=x^3$ so that the general solution is $y(x)=u_1(x)x^2+u_2(x)x^3$ where $u_1$ and $u_2$ are determined from $u_1'(x)x^2+u_2'(x)x^3)=0\\ u_1'(x)(x^2)'+u'_2(x)(x^3)'=x^2\sin x$ Hence, $u_1'=-x\sin x\\ u_2'=\sin x$ which upon integration gives $u_1(x)=x\cos x-\sin x\\ u_2(x)=-\cos x$ Thus, the given equation has general solution $y(x)=c_1x^2+c_2x^3-x^2\sin x$
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