Linear Algebra and Its Applications (5th Edition)

Published by Pearson
ISBN 10: 032198238X
ISBN 13: 978-0-32198-238-4

Chapter 5 - Eigenvalues and Eigenvectors - 5.1 Exercises - Page 273: 7

Answer

$\lambda =4$ is eigenvalue $\mathbf{v}= \left[\begin{array}{r} -1\\ -1\\ 1 \end{array}\right]$

Work Step by Step

Given $$A= \left[\begin{array}{rrr} 3 & 0 & -1 \\ 2 & 3 & 1 \\ -3 & 4 & 5 \end{array}\right]$$ Since \begin{align*} |A-\lambda I|&= 0\\ \left|\begin{array}{rrr} 3 -\lambda& 0 & -1 \\ 2 & 3-\lambda & 1 \\ -3 & 4 & 5-\lambda \end{array}\right|&= 0\\ -λ^3+11λ^2-32λ+16&=0\\ \end{align*} Since $λ=4$ satisfies the characteristic equation , then $λ=4$ is an eigenvalue and the corresponding eigenvector given by \begin{align*} \left[\begin{array}{rrr} 3-4 & 0 & -1 \\ 2 & 3-4 & 1 \\ -3 & 4 & 5-4 \end{array}\right]\left[\begin{array}{r} x_1\\ x_2\\ x_3 \end{array}\right]&=\left[\begin{array}{r} 0\\ 0\\ 0 \end{array}\right]\\ \end{align*} then $$ \left[\begin{array}{rrr} -1 & 0 & -1 \\ 2 & -1 & 1 \\ -3 & 4 & 1 \end{array}\right] \to \left[\begin{array}{rrr} -1 & 0 & -1 \\ 0 & -1 & -1 \\ 0 & 4 & 4 \end{array}\right] \to \left[\begin{array}{rrr} -1 & 0 & -1 \\ 0 & -1 & -1 \\ 0 & 0 & 0 \end{array}\right]$$ then $x_3= t,\ \ x_2=-t,\ \ x_1 = -t $, then the eigenvector is $ \left[\begin{array}{r} -1\\ -1\\ 1 \end{array}\right]$
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