x（x+y）（x-y）-x（x+y）²
=x(x+y)(x-y-x-y)
=-2xy(x+y)可以再详细吗x（x+y）（x-y）-x（x+y）²=x(x+y)[(x-y)-(x+y)]=x(x+y)(x-y-x-y)=x(x+y)*-2y=-2xy(x+y)