已知一除以X減一除以Y等於3,求3X加XY減3Y除以X減XY減Y的值.求求了

題目：

已知一除以X減一除以Y等於3,求3X加XY減3Y除以X減XY減Y的值.求求了
已知 1/X-1/Y=3，求3X+XY-3Y/X-XY-Y的值

解答：

3X+XY-3Y/(X-XY-Y)?
由1/X-1/Y=3得
y-x=3xy
x-y=-3xy
則3X+XY-3Y/X-XY-Y化簡爲
3(x-y)+xy/(x-y-xy)
=3(-3xy)+xy/(-3xy-xy)
=-8xy/(-4xy)
=2