x^2 + 7x + 12 = 0
We know that 4 times 3 is 12.
We also know that 4 plus 3 is 7.
This is all we need to know to create our two factors.
(x + 3) (x + 4) = 0
Set each factor to 0 and solve for x.
x + 3 = 0
x = - 3
x + 4 = 0
x = -4
Answer: x = - 3, x = - 4
