原式=(x^3-x)+(6x^2+12x+6)=x*(x-1)*(x+1)+6(x+1)^2=(x+1)*(x^2-x+6x+6)=(x+1)*(x+2)*(x+3)
(x^3+6x^2+11x+6) =(x^3+3x^2)+(3x^2+11x+6) =x^2(x+3)+(x+3)(3x+2) =(x+3)(x^2+3x+2)=(x+3)(x+2)(x+1)
