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 - 8.4 Complex-Valued Trial Solutions - Problems - Page 529: 7

Answer

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Work Step by Step

$y''+2y'+2y=2e^{-x}\sin x$ The complementary function is $y_c(x)=c_1 e^{-x}\sin x+c_2 e^{-x}\cos x$ We consider the complex differential equation $z''+2z'+2z=2e^{(-1+i)x}$ An appropriate complex-valued trial solution for this differential equation is: $z_p(x)=A_0e^{(-1+i)x}$ where $A_0$ is a complex constant. so that $z _p$ is a solution if and only if $2iA_0e^{(-1+i)x}=2e^{(-1+i)x}\\ \rightarrow A_0=-\frac{i}{2}$ Hence, $z=-\frac{i}{2}xe^{(-1+i)x}$ A particular solution is: $y_p(x)=Re_{\{z_p\}}=-e^{-x}x\cos x$ so that the general solution is $y(x)=c_1e^{-x}\sin x+c_2e^{-x}\cos x x-e^{-x}x\cos x$
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