Question

若x+y分之xy=2,则-x+3xy-y分之3x-xy+3y=多少?

Answer 1

xy/(x+y)=2

(x+y)/xy=1/2

1/x+1/y=1/2

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

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

=[3(1/x+1/y)-1]/[(3-(1/x+1/y)]

=(3/2-1)/(3-1/2)

=(1/2)/(5/2)

=1/5