Question

已知x分之一减去y分之一等于5,求分式x-3xy-y分之3x+5xy-3y的值？

Answer 1

1/x-1/y=5
（y-x）/xy=5
y-x=5xy
x-y=-5xy
（3x+5xy-3y）/（x-3xy-y）=【3×（-5xy）+5xy】/（-5xy-3xy）
=-10xy/-8xy
=5/4,4,因为1/x-1/y=5
所以：
(x-3xy-y)/(3x+5xy-3y) 分式上下同时除以 xy
=(1/y-3-1/x)/(3/y+5-3/x)
=(-5-3)/(-5*3+5)
=-8/(-10)
=4/5
=0.8,2,1/x-1/y=5
y-x=5xy
x-y=-5xy
(3x+5xy-3y)/(x-3xy-y)=[3(x-y)+5xy]/[(x-y)-3xy]
=[-15xy+5xy]/[-5xy-3xy]=-10xy/-8xy
=5/4,1,