Question

八年级上册数学化简求值

已知1/x-1/y=3,求5x+3xy-5y/x-2xy-y的值。

Answer 1

把已知算式两边乘xy得到：y-x=3xy；进一步得到xy=1/3(y-x）；将要求的算式xy替换掉得到{5x+3[1/3(y-x)]-5y}/{x-2[1/3(y-x）]-y};算出来得到4（x-y）/[5/3(x-y)]=12/5

Answer 2

由已知可得：1/x - 1/y=(y-x)/(xy)=3
则有：y-x=3xy，即：x-y=-3xy
所以：
(5x+3xy-5y)/(x-2xy-y)
=[5(x-y)+3xy]/(x-y-2xy)
=(-15xy+3xy)/(-3xy-2xy)
=(-12xy)/(-5xy)
=12/5

Answer 3

已知1/x-1/y=3,
得Y-x/xy=3，
即Y-x =3xy
求5x+3xy-5y/x-2xy-y
=5(x-y) +3xy/x-y -2xy
=-5(Y-x) +3xy/-(Y-x)-2xy
=-15xy+3xy/-3xy-2xy
=-12xy/-5xy
=2.4