Find the determinant of
The determinant of A is the sum of the entries in ANY row or column of A multiplied by their respective cofactors. In this case, lets choose row 1 because there is a zero entry in the second column of the first row. (We could also choose the second column, third column, and third row since they all have a 0 entry).
The determinant of
Since a12=0 à |A|=a11C11+a13C13