因式分解一題,好易

(xy - 1)(x - 1)(y + 1) - xy
=(x2y - x - xy + 1)(y + 1) - xy
=x2y2 - xy - xy2 + y + x2y - x - xy + 1 - xy
=x2y2 - 3xy - xy2 + y + x2y - x + 1
=(y2 + y)x2 - (y2 + 3y + 1)x + (y + 1)
=y(y + 1)x2 - (y2 + 3y + 1)x + (y + 1)
=y(y + 1)x2 - [(y + 1)(y + 1) + y]x + (y + 1)
=[(y + 1)x - 1][yx - (y + 1)]
=(xy + x - 1)(xy - y - 1)

(xy-1)(x-1)(y+1)-xy
=(x^2y-x-xy+1)(y+1)-xy
=x^2y^2-xy-xy^2+y+x^2y-x-xy+1-xy
=x^2y^2+x^2y-3xy-x+y-xy^2+1