Chapter 10 - Systems of Equations and Inequalities - Chapter Review - Review Exercises - Page 814: 13

$\begin{bmatrix} 4 & -4\\ 3 & 9 \\ 4 & 4 \end{bmatrix}$

Given $A=\begin{bmatrix} 1 & 0\\ 2 & 4 \\ -1 & 2 \end{bmatrix}$, $B=\begin{bmatrix} 4 & -3 & 0 \\ 1 & 1 & -2 \end{bmatrix}$, $C=\begin{bmatrix} 3 & -4\\ 1 & 5 \\ 5 & 2 \end{bmatrix}$, We have $A+C=\begin{bmatrix} 1 & 0\\ 2 & 4 \\ -1 & 2 \end{bmatrix}+\begin{bmatrix} 3 & -4\\ 1 & 5 \\ 5 & 2 \end{bmatrix}=\begin{bmatrix} 4 & -4\\ 3 & 9 \\ 4 & 4 \end{bmatrix}$