Differential Equations and Linear Algebra (4th Edition)

Published by Pearson
ISBN 10: 0-32196-467-5
ISBN 13: 978-0-32196-467-0

Chapter 9 - Systems of Differential Equations - 9.4 Vector Differential Equations: Nondefective Coefficient Matrix - Problems - Page 608: 18

Answer

See below

Work Step by Step

Given: $\begin{bmatrix} -1 & -6\\ 3 & -5 \end{bmatrix}$ A straightforward calculation yields $\det (A-\lambda I)=\begin{vmatrix} -1-\lambda & -6\\ 3 & -5-\lambda \end{vmatrix}=\lambda^2-4\lambda+13$ so that A has eigenvalues $\lambda_1=2+3i\\ \lambda_2=2-3i$ Eigenvalue $λ_1 =2+3i$: In this case, the system $(A − \lambda I)v = 0$ is $v_1=-1+i\\ v_2=1$ The solution is $v = r(-1+i,1)$. Therefore, $v_1= e^{(2+3i)t}\begin{bmatrix} -1+i\\ 1 \end{bmatrix}=e^{2t}(\cos 3t+i\sin 3t)\begin{bmatrix} -1+i\\ 1 \end{bmatrix}=e^{2t}\begin{bmatrix} -\cos 3t-\sin 3t+i(\cos 3t-\sin 3t)\\ \cos 3t+i\sin 3t \end{bmatrix}$ Hence, the general solution to the given equation is $x(t)=c_1v_1+c_2v_2=c_1e^{2t}\begin{bmatrix} -\cos 3t-\sin 3t\\ \cos 3t \end{bmatrix}+c_2e^{2t}\begin{bmatrix} -\cos 3t-\sin 3t\\ \sin 3t \end{bmatrix}$ Since \begin{bmatrix} 2\\ 2 \end{bmatrix} we obtain: $-c_1+c_2=2\\ c_1=2$ then $c_1=2\\ c_2=4$ Hence, $x(t)=2e^{2t}\begin{bmatrix} -\cos 3t-\sin 3t\\ \cos 3t \end{bmatrix}+4e^{2t}\begin{bmatrix} -\cos 3t-\sin 3t\\ \sin 3t \end{bmatrix}=e^{2t}\begin{bmatrix} -2\cos 3t-6\sin 3t\\ 2\cos 3t+4\sin 3t \end{bmatrix}$
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