Question

若x分之1-y分之1=1,求x-xy-y分之3y-xy-3x的值.

Answer 1

1/x-1/y=1

y-x=xy

x-y=-xy

(3y-xy-3x)/(x-xy-y)

=(3xy-xy)/(-xy-xy)

=2xy/(-2xy)

=-1