Chapter 10 - 10.2 - Operations with Matrices - 10.2 Exercises - Page 725: 61

Av = $\begin{bmatrix} 4\\ -2\\ \end{bmatrix}$ The transformation is a reflection across the x-axis.

First rewrite the vector as a matrix: v = $\begin{bmatrix} 4\\ 2\\ \end{bmatrix}$ Then multiply the two matrices to find Av: Av = $\begin{bmatrix} 1(4) + 0(2)\\ 0(4) + (-1)(2)\\ \end{bmatrix}$ = $\begin{bmatrix} 4\\ -2\\ \end{bmatrix}$ The transformation is a reflection across the x-axis.