题目内容
已知函数
.
(Ⅰ)若函数在区间
上有最小值
,求
的值.
(Ⅱ)若同时满足下列条件①函数
在区间
上单调;②存在区间
使得
在
上的值域也为
;则称
为区间
上的闭函数,试判断函数
是否为区间
上的闭函数?若是求出实数
的取值范围,不是说明理由.
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823202157812797.png)
(Ⅰ)若函数在区间
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823202157827391.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823202157843271.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823202157874312.png)
(Ⅱ)若同时满足下列条件①函数
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823202157890447.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823202157921315.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823202157936579.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823202157890447.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823202157983432.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823202157983432.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823202157890447.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823202157921315.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823202157812797.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823202158077560.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823202157874312.png)
(Ⅰ)
,对称轴![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823202158124394.png)
①当
时,
,解得
,(舍去)
②当
时,
,解得
,(舍去)
③当
时,
,解得
.
由①②③可得
-----------------4分
(Ⅱ)当
时,函数
在
上是闭函数.-------6分
∵函数开口向上且对称轴为
,
∴
在
上单调递增.
设存在区间
使得
在
上的值域也为![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823202159060437.png)
则有
,即方程
在
有两不同实数根 -8分
∴
,解得![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823202159153954.png)
∴
的取值范围为![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823202159184925.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/201408232021581081103.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823202158124394.png)
①当
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823202158280378.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/201408232021582951048.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823202158311395.png)
②当
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823202158326488.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/201408232021583421019.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823202158467555.png)
③当
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823202158670444.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/201408232021587161071.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823202158732540.png)
由①②③可得
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823202158732540.png)
(Ⅱ)当
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/201408232021588881063.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823202157812797.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823202158077560.png)
∵函数开口向上且对称轴为
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823202158124394.png)
∴
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823202157812797.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823202158077560.png)
设存在区间
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823202159013775.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823202157890447.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823202159060437.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823202159060437.png)
则有
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/201408232021590911123.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823202159106658.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823202158077560.png)
∴
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/201408232021591381824.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823202159153954.png)
∴
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823202157874312.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823202159184925.png)
略
![](http://thumb2018.1010pic.com/images/loading.gif)
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