题目内容
设函数
,其中
,区间![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015523926824.png)
(Ⅰ)求
的长度(注:区间
的长度定义为
);
(Ⅱ)给定常数
,当
时,求
长度的最小值.
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015523895896.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015523911388.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015523926824.png)
(Ⅰ)求
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015523942265.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015523958549.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015523958440.png)
(Ⅱ)给定常数
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015523989584.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015523989574.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015523942265.png)
(Ⅰ)
(Ⅱ)![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015524067670.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015524020663.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015524067670.png)
(1)令![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015524067942.png)
解得
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015524098596.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408240155241141059.png)
的长度![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015524020663.png)
(2)
则
由 (1)![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015524348555.png)
,令
,得
,由于![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015524426455.png)
故
关于
在
上单调递增,在
上单调递减.,
必定在
或
处取得
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408240155245821636.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015524628894.png)
因此当
时,
在区间
上取得最小值
.
第(1)题求解一元二次不等式确定区间
的取值范围,根据题意能够求出
的长度,简单题;第(2)题要能理解其实就是求
关于
在给定区间内的最小值,通过求导就能确定最小值是当
取何值,但此题易错点在于需要比较
在
与
处
的大小,利用作差或作商都可以解决,出题思路比较新颖,容易迷惑,但只要能够理解题意,基本能够求解出来.
【考点定位】考查二次不等式的求解,以及导数的计算和应用,并考查分类讨论思想和综合运用数学知识解决问题的能力.
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015524067942.png)
解得
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015524082404.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015524098596.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408240155241141059.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015524145291.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015524020663.png)
(2)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015524316594.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015524332738.png)
由 (1)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015524348555.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015524379828.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015524394376.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015524410337.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015524426455.png)
故
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015523942265.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015524457283.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015524488462.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015524504485.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015523942265.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015524535444.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015524566457.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408240155245821636.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015524597427.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015524628894.png)
因此当
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015524535444.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015523942265.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015524675502.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015524067670.png)
第(1)题求解一元二次不等式确定区间
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015523942265.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015523942265.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015523942265.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015524457283.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015524457283.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015524457283.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015524816352.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015524831368.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015523942265.png)
【考点定位】考查二次不等式的求解,以及导数的计算和应用,并考查分类讨论思想和综合运用数学知识解决问题的能力.
![](http://thumb2018.1010pic.com/images/loading.gif)
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