x^3-2x^2-7x-4 =x^3+x^2-3x^2-7x-4 =x^3+x^2-(3x^2+7x+4) =(x+1)x^2 -(3x+4)(x+1) =(x+1)(x^2 -3x -4) =(x+1)(x+1)(x-4)