Q.

If  Δ=|a11a12a13a21a22a23a31a32a33| and Aij is the cofactor of aij, then the value of Δ is given by:

1 a11A31+a12A32+a13A33  
2 a11A11+a12A21+a13A31  
3 a21A11+a22A12+a23A13  
4 a11A11+a21A21+a31A31  

Ans.

(4)

Ans.    a11A11+a21A21+a31A31

Explanation:

∆= sum of the products of the elements of any row (or any column) with their corresponding cofactors.

∴                Δ=a11A11+a21A21+a31A31