题目内容
已知函数![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824025252936777.png)
(1)若
在[-3,2]上具有单调性,求实数
的取值范围。
(2)若
的
有最小值为-12,求实数
的值;
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824025252936777.png)
(1)若
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824025252952563.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824025252968313.png)
(2)若
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824025252952563.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824025252999520.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824025252968313.png)
(1)
或
;(2)
或![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824025253061414.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824025253014496.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824025253046457.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824025253046406.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824025253061414.png)
试题分析:(1)二次函数的单调性与对称轴有关,单调区间在对称轴的一侧,可数形结合解题;
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824025252936777.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824025253108528.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824025253124431.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824025253139562.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824025253124431.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824025253139562.png)
(2)二次函数在区间上的最值在端点处或顶点处,遇到对称轴或区间含有待定的字母,则要按对称轴在不在区间内以及区间中点进行讨论.
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824025252936777.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824025253108528.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824025253217519.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824025253217519.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824025253139562.png)
试题解析:
(1)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824025253264803.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824025253108528.png)
又
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824025253280590.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824025253124431.png)
所以
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824025253311569.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824025253326568.png)
即
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824025253014496.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824025253046457.png)
(2) 由
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824025253139562.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824025253217519.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824025253404336.png)
Ⅰ.当
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824025253420563.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824025253436460.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/201408240252534511285.png)
解得:
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824025253046406.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824025253061414.png)
Ⅱ.当
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824025253482567.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824025253498453.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/201408240252535141024.png)
解得:
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824025253529409.png)
综上所述:
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824025253046406.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824025253061414.png)
![](http://thumb.zyjl.cn/images/loading.gif)
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