题目内容
已知函 数
.
(1)若曲线
在点
处的切线与直线
垂直,求函数
的单调区间;
(2)若对于
都有
成立,试求
的取值范围;
(3)记
.当
时,函数
在区间
上有两个零点,求实数
的取值范围.
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408240150315191066.png)
(1)若曲线
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015031535562.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015031551552.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015031566505.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015031535562.png)
(2)若对于
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015031613718.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015031629727.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015031644283.png)
(3)记
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015031660907.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015031691337.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015031707442.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015031722393.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015031738299.png)
(1)
的单调增区间是
,单调减区间是
.
(2)
. (3)![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015031847609.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015031769447.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015031785552.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015031816477.png)
(2)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015031816567.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015031847609.png)
试题分析:解: (I) 直线
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015031566505.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015031769447.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015031894535.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015031925820.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015031941835.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015031691337.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015031972789.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015031987730.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015032003570.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015032050407.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015032065560.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015032097481.png)
所以
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015031769447.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015031785552.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015031816477.png)
(II)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015032159982.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015032003570.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015032190519.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015032065560.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015032221610.png)
所以
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015031769447.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015032253660.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015032253588.png)
所以当
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015032268492.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015031769447.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015032315773.png)
因为对于
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015031613718.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015031629727.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015032362797.png)
则
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408240150324871034.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015032502594.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015032518596.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015031644283.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015031816567.png)
(III)依题得
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015032565926.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015032580817.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015032580565.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015032596360.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015032627554.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015032627435.png)
所以函数
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015031707442.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015032658432.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015032674516.png)
又因为函数
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015031707442.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015031722393.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408240150327211093.png)
解得
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015032736680.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015031738299.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824015031847609.png)
点评:主要是考查了运用导数研究函数的单调性,以及函数的零点问题,属于中档题。
![](http://thumb2018.1010pic.com/images/loading.gif)
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