已知(1/x)-(1/y)=5,求(6x+7xy-6y)/(8y-9xy-8y)

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1/X-1/y=5
y-x=5xy
x-y=-5xy
(6x+7xy-6y)/(8x-9xy-8y)
=6(x-y)+7xy/8(x-y)-9xy
=-30xy+7xy/-40xy-9xy
=-23/-49
=23/49