Find the determinant of

det(A)=

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, let’s 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 a_{12}=0 à |A|=a_{11}C_{11}+a_{13}C_{13}

C_{11}=(-1)^{1+1}M_{11}=M_{11}=8

C_{13}=(-1)^{1+3}M_{13}=M_{13}=6

|A|=a_{11}C_{11}+a_{13}C_{13}=3(8)+1(6)=30