Question

if element of a row is multiplied with the cofactor of any other row then the sum is

Answer 1

why is it that when I add up the product of cofactors for one row and a corresponding elements of any other row, the answer is 0?For example:
[2 3 4]
[1 2 6]
[2 1 3]
cof(2)×1 +cof(3)×2 +cof(4)×6
=0×1 -(-9)×2 +(-3)×6
18-18
=0.