因式分解6和8

6、4（x-y+1)+y(y-2x)
=4x-4y+4+y^2-2xy
=4x-2xy+(y^2-4y+4)
=2x(2-y)+(y-2)^2
=(y-2)(-2x+y-2)
8x^3-9x+8
=x^3-1-9x+9
=(x-1)(x^2+x+1)-9(x-1)
=(x-1)(x^2+x-8)