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 - 8.9 Reduction of Order - Problems - Page 573: 14

Answer

$y(x)=C_1xe^{2x}+C_2e^{2x}+x^2e^{2x}(2\ln x-3)$

Work Step by Step

Given $y''-4y'+4y=4e^{2x}\ln x$ with $y_1=e^{2x}$ We first compute the appropriate derivatives $y'=e^{2x}(u'+u)=e^{2x}u'+2e^{2x}u\\ y''=e^{2x}(u''+2u'-u)=e^{2x}u''+4e^{2x}u'$ Substituting these expressions into the given equation, we find that $u$ must satisfy $e^{2x}u''+4e^{2x}u'-4(e^{2x}u'+2e^{2x}u)+4+e^{2x}u=4e^{2x}\ln x$ which simplifies to $e^{2x}u''=4e^{2x}\ln x$ or equivalently $u''=4\ln x$ Then $u'=4x\ln x+4x+C_1$ where $C_1$ is a integration constant. Obtain: $u=2x^2\ln x-3x^2+C_1x+C_2$ The general solution is $y(x)=C_1xe^{2x}+C_2e^{2x}+x^2e^{2x}(2\ln x-3)$
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