答案:-1 原式=(x+y)(x^2+y^2)/(x^2+y^2))(x^2-y^2)=(x+y)/(x^2-y^2)=)=(x+y)/(x+y)(x-y)=x-y 将值代入即可 好列
约分分母剩下x-y,所以为-1