Question 5.2.6: Define the linear operator T: R³→ R³ by T([x1 x2 x3 ] = [ 3x...

Define the linear operator T: R³→ R³ by

T\left(\begin{bmatrix} x_{1} \\ x_{2} \\ x_{3} \end{bmatrix} \right)  = \begin{bmatrix} 3x_{1}-x_{2} + 2x_{3} \\ 2x_{1} + 2x_{3} \\ x_{1} + 3x_{2} \end{bmatrix}

Show that T is diagonalizable

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Let B = \begin{Bmatrix}e_{1}, &e_{2}, &e_{3}\end{Bmatrix} be the standard basis for R³. Then the matrix for T relative to B is

\left[T\right] _{B} = \begin{bmatrix} 3&-1&2 \\2&0&2 \\ 1&3&0 \end{bmatrix}

Observe that the eigenvalues of \left[T\right] _{B}  are  \lambda _{1} = −2 ,  \lambda _{2} = 4 ,  and   \lambda _{3} = 1  with corresponding eigenvectors, respectively

v_{1}= \begin{bmatrix} 1 \\1 \\ -2 \end{bmatrix}   v_{2}=  \begin{bmatrix} 1 \\1 \\ 1 \end{bmatrix}     and     v_{3}=  \begin{bmatrix} -5 \\4 \\ 7 \end{bmatrix}

Now let   B^{\prime} = \begin{Bmatrix}v_{1}, &v_{2}, &v_{3}\end{Bmatrix} and

P =\begin{bmatrix} 1&1&-5 \\1&1&4 \\ -2&1&7 \end{bmatrix}

Then

\left[T\right] _{B^{\prime } }= \frac{1}{9}  \begin{bmatrix} -1&4&-3 \\5&1&3\\ -1&1&0 \end{bmatrix} \begin{bmatrix} 3&-1&2 \\2&0&2 \\ 1&3&0 \end{bmatrix} \begin{bmatrix} 1&1&-5 \\1&1&4 \\ -2&1&7 \end{bmatrix} = \begin{bmatrix} -2&0&0 \\0&4&0\\ 0&0&1 \end{bmatrix}

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