Question

若1/X-1/Y=3,则2X+XY-2Y/X-2XY-Y=?

Answer 1

1/X-1/Y=3

(2X+XY-2Y) / (X-2XY-Y)

分子分母同除以XY：

= (2/Y+1-2/X) / (1/Y-2-1/X)

= {1-2(1/X-1/Y)} / {-2-(1/X-1/Y)}

= {1-2*3} / {-2-3}

= (-5) / (-5)

=1