若1/X-1/Y=3 求5x+2xy-5y/x-4 - 知识问答

若1/X-1/Y=3 求5x+2xy-5y/x-4xy-y 的值为多少

1个回答

1/x-1/y=3
(y-x)/xy=3
y-x=3xy
x-y=-3xy
(5x+2xy-5y)/(x-4xy-y )
=[5(x-y)+2xy]/[(x-y)-4xy]
=[5*(-3xy)+2xy]/(-3xy-4xy)
=-13xy/(-7xy)
=13/7

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