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 - 7.3 Diagonalization - Problems - Page 461: 36

Answer

See below

Work Step by Step

1. Find eigenvalues: (A-$\lambda$I)$\vec{V}$=$\vec{0}$ $\begin{bmatrix} 2-\lambda & 1\\ -1 & 4-\lambda \end{bmatrix}\begin{bmatrix} v_1\\ v_2 \end{bmatrix}=\begin{bmatrix} 0\\ 0 \end{bmatrix}$ $\begin{bmatrix} 2-\lambda & 1\\ -1 & 4-\lambda \end{bmatrix}=0$ $(2- \lambda)(4-\lambda)+1=0$ $(\lambda^2-3)^2=0$ $\lambda_1=\lambda_2=3$ Hence, A is nondefective by Corollary 7.2.10. The only eigenvector are easily computed: $\lambda=3: v=r(1,1)$ Hence, $A$ is detective. We obtain matrix $J_3= \begin{bmatrix} 3 & 1\\ 0 & 3 \end{bmatrix}$ There exists a matrix $S=\begin{bmatrix} v_1,v_2 \end{bmatrix}$ such that $S^{-1}AS =J_3$ Now we assume $v_1=(1,1)\\ v_2=(a,b)$ From exercise 35, we have $(A-\lambda 1)v_2=v_1$ then $\begin{bmatrix} -1 & 1\\ -1 & 1 \end{bmatrix}\begin{bmatrix} a\\ b \end{bmatrix}=\begin{bmatrix} 1\\ 1 \end{bmatrix} \\ \rightarrow -a+b=1$ Hence, $S=\begin{bmatrix} 1 & b-1\\ 1 & b \end{bmatrix}$
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