Answer: 2x^3 - x^2 - 12x - 18
Explanation:
Cross multiply, so you get
(x+4)×(x^2+x-12) = x^3 + x^2 - 12x + 4x^2 + 4x - 48
(x-3)×(x^2+x-12) = x^3 - 3x^2 - 10x - 3x^2 + 6x + 30
Add like terms together
x^3 + x^3 = 2x^3
x^2 - 3x^2 +4x^2 - 3x^2 = -x^2
-12x - 10x +4x +6x + -12x
30 - 48 = -18
So you get the big equation:
2x^3 - x^2 - 12x - 18