#### Answer

$ad-bc$

#### Work Step by Step

The determinant for a 2 by 2 matrix can be computed as:
$Determinant (Det)= \begin{vmatrix} a & b \\
c & d \\ \end{vmatrix}=ad-bc$
Let us consider an example:
$Det=\begin{vmatrix} 6 & 4 \\
-1 & 3 \\ \end{vmatrix}=(6)(3) -(4)(-1)=18+4=22$
So, our answer is: $ad-bc$