名校
解题方法
1 . 已知函数
的定义域为D,且
同时满足以下条件:
①
在D上是单调递增或单调递减函数;
②存在闭区间![](https://staticzujuan.xkw.com/quesimg/Upload/formula/4776c85b79df196f606d3ebf3697fbc3.png)
D(其中
),使得当
时,
的取值集合也是
.那么,我们称函数
(
)是闭函数.
(1)判断
是不是闭函数?若是,找出条件②中的区间;若不是,说明理由.
(2)若
是闭函数,求实数
的取值范围.
(注:本题求解中涉及的函数单调性不用证明,直接指出是增函数还是减函数即可)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/51c530f4b7491b95acb8ce3eef9aa09d.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/4fe7d5809da02c15a43a0e9a898b9086.png)
①
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/4fe7d5809da02c15a43a0e9a898b9086.png)
②存在闭区间
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/4776c85b79df196f606d3ebf3697fbc3.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/b980d8446f130dfc405c196109e73ea4.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/c6a46e678bf9d2df5ad4c782b3dc22f5.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/70128385b9ab66ac44614af35a0dcdce.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/4fe7d5809da02c15a43a0e9a898b9086.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/4776c85b79df196f606d3ebf3697fbc3.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/51c530f4b7491b95acb8ce3eef9aa09d.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/e02cab1add26335b3cb43d5b54c7c853.png)
(1)判断
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/4e16b22f8a70465aacea1cc8878777eb.png)
(2)若
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/50254ea7b079bc99aa41ad6e79252df0.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/f0a532e15e232cb4b99a8d4d07c89575.png)
(注:本题求解中涉及的函数单调性不用证明,直接指出是增函数还是减函数即可)
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