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: 19

Answer

See below

Work Step by Step

Given: $\begin{bmatrix} 2 &-1 & 3\\ 3 & 1 & 0 \\ 2 & -1 & 3 \end{bmatrix}$ A straightforward calculation yields $\det (A-\lambda I)=\begin{vmatrix} -2-\lambda & 3\\ 3 & 1-\lambda & 0 \\ 2 & -1 & 3-\lambda \end{vmatrix}=\lambda(\lambda-4)(\lambda-2)$ so that A has eigenvalues $\lambda_1=0\\ \lambda_2=4\\ \lambda_3=2$ Eigenvalue $λ_1 =0$: In this case, the system $(A − \lambda I)v = 0$ is $5v_2-9v_3=0\\ 2v_1-v_2+3v_3=0$ With $v_3=5\\ \rightarrow v_1=-3\\ v_2=9$ The solution is $v = r(-3,9,5)$. Therefore, $v_1= \begin{bmatrix} -3\\ 9\\ 5 \end{bmatrix}$ Eigenvalue $\lambda_2 =4$: In this case, the system $(A − \lambda I)v = 0$ is $v_2-v_3=0\\ v_1-v_3=0$ With $v_3=1\\ \rightarrow v_1=1\\ v_2=1$ The solution is $v = r(1,1,1)$. Therefore, $v_2=e^{4t} \begin{bmatrix} 1\\ 1\\ 1 \end{bmatrix}$ Eigenvalue $\lambda_3 =2$: In this case, the system $(A − \lambda I)v = 0$ is $v_2-3v_3=0\\ v_1-v_3=0$ With $v_3=1\\ \rightarrow v_1=1\\ v_2=3$ The solution is $v = r(1,3,1)$. Therefore, $v_3=e^{2t} \begin{bmatrix} 1\\ 3\\ 1 \end{bmatrix}$ Hence, the general solution to the given equation is $x(t)=c_1v_1+c_2v_2=c_1\begin{bmatrix} -3\\ 9\\ 5 \end{bmatrix}+c_2e^{4t}\begin{bmatrix} 1\\ 1\\ 1 \end{bmatrix}+c_3e^{2t}\begin{bmatrix} 1\\ 3\\ 1 \end{bmatrix}=\begin{bmatrix} -3c_1+c_2e^{4t}+c_3e^{2t}\\ 9c_1+c_2e^{4t}+3c_3e^{2t}\\ 5c_1+c_2e^{4t}+c_3e^{2t} \end{bmatrix}$ Since \begin{bmatrix} -4\\ 4\\ 4 \end{bmatrix} we obtain: $c_3=-2\\ 2c_2+3c_3=-4\\ -3c_1+c_2+c_3=-4$ then $c_1=1\\ c_2=1\\ c_3=-2$ Hence, $x(t)=\begin{bmatrix} -3+e^{4t}-2e^{2t}\\ 9+e^{4t}-6e^{2t}\\ 5+e^{4t}-2e^{2t} \end{bmatrix}$
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