7x^4+20x^3+11x^2+40x-6
=7x^4+21x^3-x^3-3x^2+14x^2+42x-2x-6
=7x^3(x+3)-x^2(x+3)+14x(x+3)-2(x+3)
=(x+3)(7x^3-x^2+14x-2)
=(x+3)[x^2(7x-1)+2(7x-1)]
=(x+3)(7x-1)(x^2+2)