Find the cofactor of the element a21 in the determinant
\({\rm{\Delta }} = \left| {\begin{array}{*{20}{c}} {{a_{11}}}&{{a_{12}}}&{{a_{13}}}\\ {{a_{21}}}&{{a_{22}}}&{{a_{23}}}\\ {{a_{31}}}&{{a_{32}}}&{{a_{33}}} \end{array}} \right|\)
1
a12 a33 + a13 a32
2
–a12 a33 - a13 a32
3
–a12 a33 + a13 a32
4
a22 a33 – a23 a32