计算:(1a+2-1a-2)÷4a2,并求出a=-1时的值.-数学

题目简介

计算:(1a+2-1a-2)÷4a2,并求出a=-1时的值.-数学

题目详情

计算:(
1
a+2
-
1
a-2
4
a2
,并求出a=-1时的值.
题型:解答题难度:中档来源:不详

答案

(class="stub"1
a+2
-class="stub"1
a-2
)÷class="stub"4
a2

=[class="stub"a-2
(a+2)(a-2)
-class="stub"a+2
(a+2)(a-2)
]•
a2
4

=class="stub"-4
(a+2)(a-2)
a2
4

=-
a2
(a+2)(a-2)

当a=-1时,原式=-
(-1)2
(-1+2)(-1-2)
=class="stub"1
3

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