已知1/x-1/y=3,则5x+xy-5y/x-xy-y等于

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已知1/x-1/y=3,则5x+xy-5y/x-xy-y等于
已知1/x-1/y=3,则5x+xy-5y/x-xy-y等于

已知1/x-1/y=3,则5x+xy-5y/x-xy-y等于
1/x-1/y=(y-x)/xy=3
y-x=3xy
所以x-y=-3xy
所以原式=[5(x-y)+xy]/[(x-y)-xy]
=[5(-3xy)+xy]/[(-3xy)-xy]
=-14xy/(-4xy)
=7/2

(1/x)-(1/y)=3,化成式子（y-x)/xy=3.
即得X-Y=-3XY
5x+xy-5y/x-xy-y化成式子[5（x-y）+xy]/[(x-y)-xy]
然后把X-Y=-3XY代入上式，得
(-15xy+xy)/-3xy-xy
-14xy/-4xy=7/2

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