Question:
If $A=\left[\begin{array}{ll}4 & 3 \\ 1 & 2\end{array}\right]$ and $B=\left[\begin{array}{r}-4 \\ 3\end{array}\right]$, write $A B$.
Solution:
$A B=\left[\begin{array}{ll}4 & 3 \\ 1 & 2\end{array}\right]\left[\begin{array}{c}-4 \\ 3\end{array}\right]$
$\Rightarrow A B=\left[\begin{array}{c}-16+9 \\ -4+6\end{array}\right]$
$\Rightarrow A B=\left[\begin{array}{c}-7 \\ 2\end{array}\right]$