x³-2x²-5x²+4x+12=0
x²(x-2)-(5x²-4x-12)=0
x²(x-2)-(5x+6)(x-2)=0
(x-2)(x²-5x-6)=0
(x-2)(x-6)(x+1)=0
x=2,x=6,x=-1