Notation
det means determinant | | also means determinant
Pre-Requisite
The matrix has to be 2 x 2 to be done by hand any other dimensions use calculator to solve
2 x 2
det a b c d
To find the determinant do ad - bc
Example
det 2 1 -2 3
ad - bc
(2)(3) - (1)(-2)
6 - (-2) = 8