Question

化简求值，y(x-y)-x(x+y)/x²-y² ÷ x²+y²/x+y 其中x=2，y=-1

Answer 1

您好：

y(x-y)-x(x+y)/x²-y² ÷ x²+y²/x+y
=(xy-y²-x²-xy)/(x+y)(x-y)÷（x²+y²）/(x+y)
=-(x²+y²)/(x-y)÷(x²+y²)
=1/(y-x)
=1/(-1-2)
=-1/3

不明白，可以追问如有帮助，记得采纳，
谢谢 祝学习进步！

Answer 2

解：
原式=yx-y²-x²-xy/(x-y)(x+y) ÷( x²+y²)/x+y
=-y²-x²/(x-y)(x+y)×x+y/( x²+y²)
=-(x²+y²)/(x-y)(x+y)×x+y/( x²+y²)
=-1/(x-y)
=1/(y-x)
将x=2，y=-1代入
原式=1/(-1-2)
=-1/3