The product of the cofactors of 3 and -2 in the matrix [10−23−12456]\begin{bmatrix}1 & 0 & -2 \\3 & -1 & 2 \\4 & 5 & 6\end{bma
Question
The product of the cofactors of 3 and -2 in the matrix 1340−15−226 is:
A.
180
B.
190
C.
-190
D.
-180
Correct option is C
Cofactor of 3 (element at (2,1))The cofactor of element a21=3 is:C21=(−1)2+1⋅det(05−26)det(05−26)=(0)(6)−(−2)(5)=10Thus,C21=(−1)3⋅10=−10Cofactor of -2 (element at (1,3))The cofactor of element a13=−2 is:C13=(−1)1+3⋅det(34−15)det(34−15)=(3)(5)−(−1)(4)=15+4=19Thus,C13=(−1)4⋅19=19Product of the cofactorsThe product of the cofactors is:C21⋅C13=(−10)⋅19=−190