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