问题 解答题
先化简再求值:
x-3
2x-4
÷
x2-9
x-2
,其中x=-5.
答案

x-3
2x-4
÷
x2-9
x-2

=

x-3
2x-4
x-2
x2-9

x-3
2(x-2)
x-2
(x+3)(x-3)

=

1
2(x+3)

当x=-5时,原式=

1
2(-5+3)
=-
1
4

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