[m]\begin {bmatrix}-1&8\\-3&2\end {bmatrix}\cdot\begin {bmatrix}a-5&3a\\-2&4\end {bmatrix}=\begin {bmatrix}-1\cdot (a-5)+8\cdot (-2) &-1\cdot (3a)+8\cdot 4\\-3\cdot (a-5)+2\cdot (-2)&-3\cdot 3a+2\cdot 4\end {bmatrix}=\begin {bmatrix}-a+5-16 &-3a+32\\-3a+15-4&-9a+8\end {bmatrix}=\begin {bmatrix}-a-11 &-3a+32\\-3a+11&-9a+8\end {bmatrix} [/m]
