2xy/x平方-y平方-x/x+y+y/y-x,其中x=3、y=2 先化简再求值
问题描述：
2xy/x平方-y平方-x/x+y+y/y-x,其中x=3、y=2 先化简再求值
答
2xy/x平方-y平方-x/x+y+y/y-x
=[2xy-x(x-y)-y(x+y)]/(x+y)(x-y)
=（2xy-x²+xy-xy-y²）/(x+y)(x-y)
=(2xy-x²-y²)/(x+y)(x-y)
=-(x-y)²/(x+y)(x-y)
=(y-x)/(x+y)
=（2-3）/(3+2)
=-1/5
不明白，可以追问
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答
2xy/(x^2-y^2)-x/(x+y)+y/(y-x)=2xy/(x^2-y^2)-x/(x+y)-y/(x-y)=2xy/[(x-y)(x+y)]-x(x-y)/[(x-y)(x+y)]-y(x+y)/[(x-y)(x+y)]=[2xy-x(x-y)-y(x+y)]/[(x-y)(x+y)]=[2xy-x^2+xy-xy-y^2]/[(x-y)(x+y)]=-[x^2+y^2-2xy]/[(...