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 - 9.3 General Results for First-Order Linear Differential Systems - Problems - Page 598: 6

Answer

See below

Work Step by Step

Given: $x_1(t)=\begin{bmatrix} 2t\\ e^t \end{bmatrix}$ $x_2(t)=\begin{bmatrix} 0\\ 3e^{t} \end{bmatrix}$ $A=\begin{bmatrix} \frac{1}{t} & 0\\ 0 & 1 \end{bmatrix}$ Differentiating the given vector functions with respect to t yields, $x_1'(t)=\begin{bmatrix} 2\\ e^t \end{bmatrix}$ $x_2'(t)=\begin{bmatrix} 0\\ 3e^{t} \end{bmatrix}$ whereas $Ax_1(t)=\begin{bmatrix} \frac{1}{t} & 0\\ 0 & 1 \end{bmatrix}\begin{bmatrix} 2t\\ e^t \end{bmatrix}=\begin{bmatrix} 2\\ e^t \end{bmatrix}=x_1'(t)$ $Ax_2(t)=\begin{bmatrix} \frac{1}{t} & 0\\ 0 & 1 \end{bmatrix}\begin{bmatrix} 0\\ 3e^{t} \end{bmatrix}=\begin{bmatrix} 0\\ 3e^{t} \end{bmatrix}=x_2'(t)$ The Wronskian of these solutions is $W_{[x_1,x_2]}(t)=\begin{vmatrix} 2t & 0\\ e^{t} & 3e^{t} \end{vmatrix}=6te^{t}$ Since the Wronskian is never zero, it follows that $\{x_1, x_2\}$ is linearly independent on any interval and so is a fundamental set of solutions for the given vector differential equation. Therefore, the general solution to the system is $x(t)=\begin{bmatrix} 2c_1t \\ c_1e^{t}+3c_2e^{t} \end{bmatrix}$
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