已知1/x-1/y=3，求代数式2x-14xy-2y/x-2xy-y的值

Answer 1

解：
由1/x-1/y=1,变形
两边各乘以xy，得，y-x=3xy,∴xy=1/3(y-x),
（2x-14xy-2y）/（x-2xy-y）
=[2x-14/3(y-x)-2y]/ [ x-2/3(y-x)-y) ],
分式上下各乘以3，并展开括号，得
3(2x-14/3y+14/3x-2y)/3(x-2/3y+2/3x-y)
=(6x-14y+14x-6y)/(3x-2y+2x-3y)
=(20x-20y)/(5x-5y)
=4(5x-5y)/(5x-5y)
=4

祝学习进步

Answer 2

1/x-1/y=1,两边各乘以xy，得，y-x=3xy,
∴xy=1/3(y-x),
（2x-14xy-2y）/（x-2xy-y）
=[2x-14/3(y-x)-2y]/ [ x-2/3(y-x)-y) ],
分式上下各乘以3，得
3(2x-14/3y+14/3x-2y)/3(x-2/3y+2/3x-y)
=(6x-14y+14x-6y)/(3x-2y+2x-3y)
=(20x-20y)/(5x-5y)
=4(5x-5y)/(5x-5y)
=4

Answer 3

解题：根据已知条件，得（y-x)/xy=3 → (y-x)=3xy
2x-14xy-2y/x-2xy-y=2(x-y)-14xy/(x-y)-2xy
=-6xy-14xy/-3xy-2xy
=4

Answer 4

1/x-1/y=3
(y-x)/xy=3
y-x=3xy
x-y=-3xy

(2x-14xy-2y)/(x-2xy-y)
=[2(x-y)-14xy]/(x-y-2xy)
=[2*(-3xy)-14xy]/(-3xy-2xy)
=(-20xy)/(-5xy)
=4

Answer 5

解：已知1/x-1/y=3，那么，y-x=3xy
即： (2x-14xy-2y)/(x-2xy-y)
=-20xy/(xy)
=-20 。

追问

别人都说是4耶！

就你说是20，别人都说是4耶！

追答

哦，丢不起，我算错了。
解：已知1/x-1/y=3，那么，y-x=3xy
即： (2x-14xy-2y)/(x-2xy-y)
=-20xy/(-2xy-3xy)
=4 .