$ A=\left[\begin{array}{cccc}1&2&3&4\\5&6&7&8\end{array}\right] B=\left[\begin{array}{cccc}1&2\\3&4\end{array}\right] $
$ AB = \left[\begin{array}{cccc}1&2&3&4\\5&6&7&8\end{array}\right] \left[\begin{array}{cccc}1&2\\3&4\end{array}\right] \definecolor{orange}{RGB}{255,165,0}\pagecolor{orange}e^{i \pi} + 1 = 0 $
