χ-y+2y∧2/x+y
=[(x-y)(x+y)+2y^2]/(x+y)
=(x^2+y^2)/(x+y)你第二步【(x-y)(x+y)]+2y^2]/(x+y)(x^2-y^2+2y^2)/(x+y)有这个公式吗： (x^2-y^2+2y^2)=x^2+y^2(x^2-y^2+2y^2)=x^2+y^2这个不是公式，直接计算就可以了x^2-y^2+2y^2=x^2+2y^2-y^2=x^2+y^22个y^2-1个y^2=1个y^2