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 607: 11

Answer

See below

Work Step by Step

Given: $\begin{bmatrix} 0 & -3 & 1\\ -2 & -1 & 1\\ 0 & 0 & -2 \end{bmatrix}$ A straightforward calculation yields $\det (A-\lambda I)=\begin{vmatrix} -\lambda & -3 & 1\\ -2 & -1-\lambda & 1\\ 0 & 0 & -2-\lambda \end{vmatrix}=(2-\lambda)(\lambda+3)(\lambda-2)$ so that A has eigenvalues $\lambda_1=2\\ \lambda_2=2\\ \lambda_3=-3$ Eigenvalue $λ_1 =2$: In this case, the system $(A − \lambda I)v = 0$ is $v_3=2v_1+3v_2\\ v_1=0\\ v_2=1\\ \rightarrow v_3=3$ The solution is $v = r(0,1,3)$. Therefore, $v_1=e^{2t} \begin{bmatrix} 0\\ 1 \\ 3 \end{bmatrix}$ Eigenvalue $\lambda_2 =-2$: In this case, the system $(A − \lambda I)v = 0$ is $v_3=2v_1+3v_2\\ v_1=1\\ v_2=0\\ \rightarrow v_3=2$ The solution is $v = r(1, 0,2)$. Therefore, $v_2=e^{-2t} \begin{bmatrix} 1\\ 0\\ 2 \end{bmatrix}$ Eigenvalue $\lambda_3 =-3$: In this case, the system $(A − \lambda I)v = 0$ is $v_1=v_2=1\\ v_3=0$ The solution is $v = r(1,1,0)$. Therefore, $v_3=e^{-3t} \begin{bmatrix} 1\\ 1\\ 0 \end{bmatrix}$ Hence, the general solution to the given equation is $x(t)=c_1v_1+c_2v_2+c_3v_3=c_1e^{2t}\begin{bmatrix} 0\\ 1\\ 3 \end{bmatrix}+c_2e^{2t}\begin{bmatrix} 1\\ 0\\ 2 \end{bmatrix}+c_3e^{-3t}\begin{bmatrix} 1\\ 1\\ 0 \end{bmatrix}=\begin{bmatrix} c_2e^{2t}+c_3e^{-3t}\\ c_1e^{2t}+c_3e^{-3t}\\ 3c_1e^{2t}+2c_2e^{2t} \end{bmatrix}$
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