数学 已知x分之1减y分之1等于2,求2x减5xy减2y分之3x加4xy减3y的值

1/x-1/y=2
两边乘xy
y-x=2xy
x-y=-2xy
原式=[3(x-y)+4xy]/[2(x-y)-5xy]
=[3(-2xy)+4xy]/[2(-2xy)-5xy]
=-2xy/(-9xy)
=2/9