Question

Let M = [1 -2] and N = $\left[\begin{array}{cc}2& 1\\ -1& 2\end{array}\right].$
Find MN.

Answer 1

$MN={[1-2]}_{1\times 2}{\left[\begin{array}{cc}2& 1\\ -1& 2\end{array}\right]}_{2\times 2}$

$MN={[1\times 2-2\times -11\times 1-2\times 2]}_{1\times 2}$

$MN={[2+21-4]}_{1\times 2}$

$MN={[4-3]}_{1\times 2}$