已知一除以X减一除以Y等于3,求3X加XY减3Y除以X减XY减Y的值.求求了

3X+XY-3Y/(X-XY-Y)?
由1/X-1/Y=3得
y-x=3xy
x-y=-3xy
则3X+XY-3Y/X-XY-Y化简为
3(x-y)+xy/(x-y-xy)
=3(-3xy)+xy/(-3xy-xy)
=-8xy/(-4xy)
=2