x3 - 3x2 - 4x + 12
= x2(x-3) - 4(x-3)
= (x-3)(x2 -4)
=(x-3)(x-2)(x+2)
\(x^3-3x^2-4x+12\)
\(=\left(x^3-3x^2\right)-\left(4x-12\right)\)
\(=x^2\left(x-3\right)-4\left(x-3\right)\)
\(=\left(x^2-4\right)\left(x-3\right)\)
\(=\left(x-2\right)\left(x+2\right)\left(x-3\right)\)