Differential Equations and Linear Algebra (4th Edition)

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

Chapter 7 - Eigenvalues and Eigenvectors - 7.1 The Eigenvalue/Eigenvector Problem - Problems - Page 444: 21

Answer

$\lambda_1=3$ $\vec{V}=(0,-1,1)r$ and $\lambda_2=1$ $\vec{V}=(0,1,1)r$

Work Step by Step

1. eigenvalues: (A-$\lambda$I)$\vec{V}$=$\vec{0}$ $\begin{bmatrix} 3-\lambda &0 &0 \\ 0& 2-\lambda&-1\\ 1&-1 &2-\lambda \end{bmatrix}\begin{bmatrix} v_1\\ v_2\\ v_3 \end{bmatrix}=\begin{bmatrix} 0\\ 0\\ 0 \end{bmatrix}$ $\begin{vmatrix} 3-\lambda &0 &0 \\ 0& 2-\lambda&-1\\ 1&-1 &2-\lambda \end{vmatrix}=0$ $\lambda_1=3$ and $\lambda_2=1$ =============================== 2. eigenvectors $\lambda_1=3$ let $B=A-\lambda_1I$ $B= \begin{bmatrix} 3-\lambda_1 &0 &0 \\ 0& 2-\lambda_1&-1\\ 1&-1 &2-\lambda_1 \end{bmatrix}$ = $\begin{bmatrix} 0&0&0 \\ 0 &-1 &-1\\ 1&-1 &-1 \end{bmatrix}$ Then, $B\vec{V}$=$\vec{0}$ Use reduced row echelon form $[B|\vec{0}]$= \[ \left(\begin{array}{@{}ccc|c@{}} 1 & 0 & 0 & 0 \\ 0 & 1 & 1 & 0 \\ 0 & 0 & 0 & 0 \end{array}\right) \] let $r$ is a free variable. Then $x_1=0$ $x_2=-x_3$ $\vec{V}=(0,-1,1)r$ ============================= $\lambda_2=1$ let $B=A-\lambda_2I$ $B= \begin{bmatrix} 3-\lambda_2 &0 &0 \\ 0& 2-\lambda_2&-1\\ 1&-1 &2-\lambda_2 \end{bmatrix}$ = $\begin{bmatrix} 2&0&0 \\ 0 &1 &-1\\ 1&-1 &1 \end{bmatrix}$ Then, $B\vec{V}$=$\vec{0}$ Use reduced row echelon form $[B|\vec{0}]$= \[ \left(\begin{array}{@{}ccc|c@{}} 1 & 0 & 0 & 0 \\ 0 & 1 & -1& 0 \\ 0 & 0 & 0 & 0 \end{array}\right) \] let $r$ is a free variable. Then $x_1=0$ $x_2=x_3=r$ $\vec{V}=(0,1,1)r$
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