1/x-1/y=(y-x)/xy=3
y-x=3xy
所以x-y=-3xy
原式=[3(x-y)-5xy]/[2(x-y)+3xy]
=[3(-3xy)-5xy]/[2(-3xy)+3xy]
=-14xy/(-3xy)
=14/3
1/x+1/y=3 ,求2x-3xy+2y/-3x+xy-3y
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