1/x+1/y=3 去分母得 x+y=3xy (3x-5xy+3y)/(x-2xy+y) =[3(x+y)-5xy]/(x+y-2xy)=(9xy-5xy)/(3xy-2xy)=4xy/xy=4
4
(3x-5xy+3y)/(x-2xy+y) =[(3x-5xy+3y)/(xy)]/[(x-2xy+y)/(xy)]=(3/y-5+3/x)/(1/y-2+1/x) =(3*3-5)/(3-2)=4
