先化简-2xyx2-y2÷(1x-y-1x+y),再求值,其中x=1-2.-数学

题目简介

先化简-2xyx2-y2÷(1x-y-1x+y),再求值,其中x=1-2.-数学

题目详情

先化简
-2xy
x2-y2
÷(
1
x-y
-
1
x+y
)
,再求值,其中x=1-
2
题型:解答题难度:中档来源:不详

答案

原式=class="stub"-2xy
(x+y)(x-y)
÷[class="stub"x+y
(x+y)(x-y)
-class="stub"x-y
(x+y)(x-y)
]
=class="stub"-2xy
(x+y)(x-y)
÷class="stub"2y
(x+y)(x-y)
=class="stub"-2xy
(x+y)(x-y)
(x+y)(x-y)
2y
=-x,
当x=1-
2
时,原式=-(1-
2
)=
2
-1.

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