x3-7x+6d的“x3”指的是三次方吧?
x^3-7x+6
=x^3-2x^2+x+2x^2-8x+6
=x(x-1)^2+(2x-6)(x-1)
=(x-1)[x(x-1)+2x-6]
=(x-1)(x+3)(x-2)