更新时间2019-09-17 22:12:56
好的多加50金币
解 1/x+1/y=5
两边同时乘xy,得:
x+y =5xy
整理 (2X-5XY+2Y)/(X+2XY+Y)
=[2(x+y)-5xy]/(x+y+2xy]
把x+y=5xy代入(2X-5XY+2Y)/(X+2XY+Y),得: =[10xy-5xy]/[5xy+2xy]
=(5xy)/(7xy)
=5/7 . 所以(2X-5XY+2Y)/(X+2XY+Y)的值为5/7.
1/x+1/y=5
(x+y)/xy=5
x+y=5xy
(2x-5xy+2y)/(x+2xy+y)=(2*5xy-5xy)/(5xy+2xy)=5xy/7xy=5/7
这种题首先就是提取常数,之后再化简
原式=[2(x+2xy+y)-9xy]/(x+2xy+y)=2-9xy/(x+2xy+y)
对9xy/(x+2xy+y)分子和分母同除以xy后,得
原式=2-9/(1/x+1/y+2)=2-9/7=5/7
∵1/x+1/y=5,∴y+x=5xy。
(2x-5xy+2y)/(x+2xy+y)
=[2(x+y)-5xy]/[(x+y)+2xy]
=(2*5xy-5xy)/(5xy+2xy)
=5xy/(7xy)
=5/7
1/x+1/y=5
x+y=5xy
(2x-5xy+2y)/(x+2xy+y)
=(10xy-5xy)/(5xy+2xy)
=5/7
已知1/X+1/Y=5,则X+Y=5XY,2X+2Y=10XY
(2X-5XY+2Y)/(X+2XY+Y)
=(2X+2Y-5XY)/(X+Y+2XY)
=(10XY-5XY)/(5XY+2XY)
=(5XY)/(7XY)
=5/7