Multivariable Calculus, 7th Edition

Published by Brooks Cole
ISBN 10: 0-53849-787-4
ISBN 13: 978-0-53849-787-9

Chapter 17 - Second-Order Differential Equations - 17.2 Exercises - Page 1180: 28

Answer

$y=c_1e^{-2x}+c_2 xe^{-2x}+\dfrac{e^{-2x}}{2x} $

Work Step by Step

The auxiliary solution is: $r^2+4r+1=0 \implies r=-2$ The complementary solution is: $y_c=c_1 e^{-2x}+c_2 xe^{-2x}$ The particular solution is: $y_p=u_1 e^{-2x}+u_2xe^{-2x}\implies y'_p=u'_1 e^{-2x}-2u_1 e^{-2x}+u'_2 xe^{-2x}+u_2 e^{-2x}(1-2x)$ This gives: $u'_1=-u'_2 x$ $-2u'_1+u'_2(1-2x)=\dfrac{1}{x^3}$ $u'_2=\dfrac{1}{x^3}$ and $u_2=\int \dfrac{1}{x^3}=\dfrac{-1}{2x^2}$ $u'_1=\dfrac{-1}{x^2}$ and $u_1=\int \dfrac{-1}{x^2}=\dfrac{1}{x}$ Thus, $y_p=\dfrac{e^{-2x}}{x} -\dfrac{xe^{-2x}}{2x^2} =\dfrac{e^{-2x}}{2x} $ Now, $y=y_c+y_p$ Hence, $y=c_1e^{-2x}+c_2 xe^{-2x}+\dfrac{e^{-2x}}{2x} $
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