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: 19

Answer

$y(x)=c_1x^{-2}+c_2x^{-3}-2e^{2x}(x-1)x^{-3}$

Work Step by Step

Given $x^2y''+6xy'+6y=4e^{2x}$ In this case the substitution $y(x) = x^r$ yields the indicial equation $$r(r-1)+6r+6=0\\ r^2+5r+6=0$$ 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 $u_1'(x)x^{-2}+u_2'(x)x^{-3}=0\\ u_1'(x)(x^{-2})'+u'_2(x)(x^{-3})'=4e^{2x}$ Hence, $u_1'=4xe^{2x}\\ u_2'=-4x^2e^{2x}$ which upon integration gives $u_1(x)=2xe^{2x}-e^{2x}\\ u_2(x)=-2x^2e^{2x}+2xe^{2x}-e^{2x}$ Thus, the given equation has general solution $y(x)=c_1x^{-2}+c_2x^{-3}-2e^{2x}(x-1)x^{-3}$
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