51.(2008福建福州)化简:.
解:原式=
50.(2008江苏镇江)计算化简.
解:原式····················· (1分)
····················· (2分)
···························· (4分)
. ················(5分)
49.(2008江苏扬州)课堂上,李老师出了这样一道题,
已知x=2008-5,求代数式的值,小明觉得直接代入计算太繁了,请你来帮他解决,并写出具体过程。
解:原式=
=
=
48. (08年山东省)先化简,再求值:
÷,其中,.
解:原式= ……………………………2分
= …………………………………………3分
=. ……………………………………………………………4分
当,时,
原式=.
47. (2008年江苏南充市)化简,并选择你最喜欢的数代入求值.
解:原式······················································································ 2分
·········································································································· 4分
···························································································································· 5分
选取除0与1以外的任何值,求代数式的值 6分
46.(2008江苏盐城)先化简,再求值:,其中.
解:原式
当x=-4时,原式=
45.(2008湖北孝感)请你先将式子化简,然后从1,2,3中选择一个数作为的值代入其中求值。
解:原式=
取a=2,原式=2008。(取a=3,原式=1004)
44.(2008湖北襄樊)化简求值:
43. (2008湖北武汉)先化简,再求值:,其中.
解:提示:
42. .(2008广东深圳)先化简代数式÷,然后选取一个合适的a值,代入求值.
解: 方法一: 原式=
=
=
(注:分步给分,化简正确给5分.)
方法二:原式=
=
=
取a=1,得
原式=5
(注:答案不唯一.如果求值这一步,取a=2或-2,则不给分.)
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