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: 17

Answer

$x(t)=\begin{bmatrix} e^{5t}+2e^{t}\\ -e^{5t}+e^{t} \end{bmatrix}$

Work Step by Step

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