[tex]A=\left[\begin{array}{ccc}5&-4\\3&6\end{array}\right] \\\\A_x=\left[\begin{array}{ccc}12&-4\\66&6\end{array}\right][/tex]
[tex]|A_x|=\left|\begin{array}{ccc}12&-4\\66&6\end{array}\right|=(12)(6)-(66)(-4)=72+264=336[/tex]
