已知1/x-1/y=5,求(5x+3xy-5y)/(x-2xy-y)

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1/x-1/y=5
两边乘xy
y-x=5xy
x-y=-5xy
所以原式=[5(x-y)+3xy]/[(x-y)-2xy]
=[5(-5xy)+3xy]/[(-5xy)-2xy]
=-22xy/(-7xy)
=22/7

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