Question

已知x分之1-y分之1=2,求x-xy-y分之3x+5xy-3y的值

Answer 1

(3x+5xy-3y)/(x-xy-y)=(3x-3xy-3y+8xy)/(x-xy-y)

=3+8xy/(x-xy-y)

=3+8/(1/y-1-1/x)

=3+8/(-3)=1/3