If $\mathrm{A}=\left[\begin{array}{ll}3 & 4 \\ 1 & 2\end{array}\right]$, find the value of $3|\mathrm{~A}|$.

Solution:

Find the determinant of $A$ and then multiply it by 3
$\begin{array}{l}
|A|=2 \\
3|A|=3 \times 2 \\
=6
\end{array}$