3x^5+3x^4-6x^4-6x^3-7x^3-7x^2-4x^2-4x-6x-6
=3x^4(x+1)-6x^3(x+1)-7x^2(x+1)-4x(x+1)-6(x+1)
=(3x^4-6x^3-7x^2-4x-6)(x+1)
=(3x^4+3x^3-9x^3-9x^2+2x^2+2x-6x-6)(x+1)
=(3x^3-9x^2+2x-6)(x+1)^2
=(3x^2(x-3)+2(x-3))(x+1)^2
=(3x^2+2)(x-3)(x+1)^2