x^3-13x-12=0
x^3-x-12x-12=0
x(x^2-1)-12(x+1)=0
x(x+1)(x-1)-12(x+1)=0
(x+1)(x^2-x-12)=0
(x+1)(x-4)(x+3)=0
x1=-1 x2=4 x3=-3