解：由1/x-1/y=3得y-x=3xy依题意(2x-14xy-2y)/(x-2xy-y)=[2(x-y)-14xy]/[(x-y)-2xy]=(-6xy-14xy)/(-3xy-2xy)=4
(2x-14xy-2y)/(x-2xy-y)=2-10(xy)/(x-2xy-y)=2-10/(1/y-2-1/x)=2-10/(-3-2)=4 选择或填空可以设x=1/4,y=1 带入求得4
