Given that A = (3 x, x+1 2) and B =(1 2, 3 0), find value of x for which AB is a singular matrix.

Answer 1

You want |AB| = 0
AB = (3x+3 6,x+7 2x+2)
so, solve
(3x+3)(2x+2) - 6(x+7) = 0