Question
If $A=\left[\begin{array}{ccc}4 & 3 & 1 \\ 2 & 3 & -8 \\ 1 & 0 & -4\end{array}\right], B=\left[\begin{array}{ccc}2 & 3 & 4 \\ 1 & 9 & 2 \\ -7 & 1 & -1\end{array}\right]$ and $C=\left[\begin{array}{ccc}8 & 3 & 4 \\ 1 & -2 & 3 \\ 2 & 4 & -1\end{array}\right]$ then verify that $A+(B+C)=(A+B)+C$