Exercise 2.3.12

The first productis $\left[\begin{array}{ccc}9\hfill & 8\hfill & 7\hfill \\ 6\hfill & 5\hfill & 4\hfill \\ 3\hfill & 2\hfill & 1\hfill \end{array}\right]\begin{array}{ccc}\hfill & \text{ rows and }\hfill & \hfill \\ \hfill & \text{ also columns }\hfill \end{array}$ The second productis $\left[\begin{array}{ccc}1\hfill & 2\hfill & \hfill 3\\ 0\hfill & 1\hfill & \hfill -2\\ 0\hfill & 2\hfill & \hfill -3\end{array}\right]$. 13 (a) $E$ times the third column of $B$ is the third column of $\mathit{EB}$. A column that starts at zero will stay at zero. (b) $E$ could add row 2 to row 3 to change a zero row to a nonzero row.