X三次方-xy²+x²y-y三次方
X^3-xy²+x²y-y^3
=x^2(x+y)-y^2(x+y)
=(x+y)(x^2-y^2)
=(x+y)(x-y)(x+y)
=(x+y)^2(x-y)四分之一（x-y)²+x-y+1 这道也请大师帮忙讲一下~四分之一（x-y)²+x-y+11/4(x-y)^2+x-y+1=1/4((x-y)^2+4(x-y)+4)=1/4(x-y+2)^2