1 . 若函数
在定义域区间
上连续,对任意
恒有![](https://staticzujuan.xkw.com/quesimg/Upload/formula/e1cfb878da573f79cb25c8df42b7dd8e.png)
,则称函数
是区间
上的上凸函数,若恒有
,则称函数
是区间
上的下凸函数,当且仅当
时等号成立,这个性质称为函数的凹凸性.上述不等式可以推广到取函数定义域中的任意n个点,即若
是上凸函数,则对任意
恒有
,若
是下凸函数,则对任意
恒有
,当且仅当
时等号成立.应用以上知识解决下列问题:
(1)判断函数
(
,
),
,
在定义域上是上凸函数还是下凸函数;(只写出结论,不需证明)
(2)利用(1)中的结论,在
中,求
的最大值;
(3)证明函数
是上凸函数.
![](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/e9d6fe21d6ed78bfc1d2b9cc41a766c1.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/e1cfb878da573f79cb25c8df42b7dd8e.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/53e3d9d86ac5a0f90301f8952bdc4c90.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/5a7cd59277a15b4d9063be84a40d5541.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/7f333263260646c494225db8a7476c00.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/4fe7d5809da02c15a43a0e9a898b9086.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/b36203ece868797d7f1b130ec483ebfa.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/fdddc0ae56c39e2cc1293ccca368359d.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/4fe7d5809da02c15a43a0e9a898b9086.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/b36203ece868797d7f1b130ec483ebfa.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/c6369550920162ee040faa3f81df2345.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/73223617c8855826298d435673787a94.png)
(1)判断函数
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/b1bd0587f5d6a3b5db9e4a93e0dbc0ef.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/20849c00c47cbdc43f18d53341b6c4e5.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/24a57996290794e082b21d8f1dfc322a.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/588bbf780d49cf4d29802c2e4126f112.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/4e10dce73bdc1d522ae7cb34805ed3d8.png)
(2)利用(1)中的结论,在
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/15c0dbe3c080c4c4636c64803e5c1f76.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/92e19e4be18878ebb959be989905330a.png)
(3)证明函数
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/f2cbe0018800880fbad883926a7beb77.png)
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