x³+x²-24x+36=0
x³-3x²+4x²-12x-12x+36=0
x²(x-3)+4x(x-3)-12(x-3)=0
(x-3)(x²+4x-12)=0
(x-3)(x+6)(x-2)=0
x=3或x=-6或x=2