题目内容
设函数
,
,其中实数
.
(1)若
,求函数
的单调区间;
(2)当函数
与
的图象只有一个公共点且
存在最小值时,记
的最小值为
,求
的值域;
(3)若
与
在区间
内均为增函数,求实数
的取值范围.
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824024108626874.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824024108642787.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824024108658408.png)
(1)若
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824024108658399.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824024108673491.png)
(2)当函数
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824024108689608.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824024108704585.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824024108720491.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824024108720491.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824024108736517.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824024108736517.png)
(3)若
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824024108673491.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824024108720491.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824024108798551.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824024108814277.png)
(1)详见解析;(2)
;(3)
.
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824024108829718.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824024108845769.png)
试题分析:(1)这是一个三次函数求单调区间的问题,此类问题比较熟悉,三次函数的导数为二次函数,它的零点容易求出,但要注意对零点大小的比较,才能准确写出单调区间;(2)函数
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824024108689608.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824024108704585.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824024108876562.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824024108892491.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824024108907283.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824024108892491.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824024108736517.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824024108736517.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824024108954447.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824024108798551.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824024109016442.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824024108798551.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824024108907283.png)
试题解析:(1)∵
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408240241090631585.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824024108658399.png)
∴当
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824024109079397.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824024109110527.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824024109110614.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824024109282581.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824024109297617.png)
∴
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824024108673491.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824024109344563.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824024109360787.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824024109375709.png)
(2)由题意知
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824024109391839.png)
即
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824024109406777.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824024109422539.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824024109438560.png)
又
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824024108658408.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824024108720491.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824024109500566.png)
又
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824024109531947.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824024109547677.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824024108736517.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824024108829718.png)
(3)当
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824024108658399.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824024108673491.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824024109344563.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824024109360787.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824024108720491.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824024109687748.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824024109703790.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824024109734370.png)
当
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824024109734388.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824024108673491.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824024109781775.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824024109796578.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824024108720491.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824024109828738.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824024109843885.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824024109859429.png)
综上可知,实数
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824024108907283.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824024108845769.png)
![](http://thumb2018.1010pic.com/images/loading.gif)
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