已知1x-1y=2,则5x+xy-5yx-xy-y等于()A.13B.-13C.-3D.3-数学

题目简介

已知1x-1y=2,则5x+xy-5yx-xy-y等于()A.13B.-13C.-3D.3-数学

题目详情

已知
1
x
-
1
y
=2
,则
5x+xy-5y
x-xy-y
等于(  )
A.
1
3
B.-
1
3
C.-3D.3
题型:单选题难度:中档来源:不详

答案

class="stub"1
x
-class="stub"1
y
=class="stub"y-x
xy
=2,即y-x=2xy,
∴x-y=-2xy,
class="stub"5x+xy-5y
x-xy-y
=
5(x-y)+xy
(x-y)-xy
=class="stub"-10xy+xy
-2xy-xy
=class="stub"-9xy
-3xy
=3.
故选D

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