12d^2 + 4d -1
This is a quadratic expression and we would use factorization method.
Multiply the first and the last terms 12d^2 -1 = -12d^2
Next, we think of two factors that multiply to give -12d^2 and add up to give the middle term +4d.
So the factors are 6d and -2d,
Check: 6d-2d = -12d^2
6d + (-2d) = 6d -2d = 4d
So we replace the middle term +4d with (6d - 2d)
12d^2 + 4d -1
12d^2 +6d - 2d -1
6d(2d + 1) -1(2d +1) Factorize out (2d+1)
(2d+1)(6d - 1)
(6d -1)(2d+1).
Option C.
