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1 . 函数的凹凸性的定义是由丹麦著名的数学家兼工程师Johan Jensen在1905年提出来的.其中对于凸函数的定义如下:设连续函数
的定义域为
(或开区间
或
,或
都可以),若对于区间
上任意两个数
,均有
成立,则称
为区间
上的凸函数.容易证明譬如
都是凸函数.Johan Jensen在1906年将上述不等式推广到了
个变量的情形,即著名的Jensen不等式:若函数
为其定义域上的凸函数,则对其定义域内任意
个数
,均有
成立,当且仅当
时等号成立.
(1)若函数
为
上的凸函数,求
的取值范围:
(2)在
中,求
的最小值;
(3)若连续函数
的定义域和值域都是
,且对于任意
均满足下述两个不等式:
,证明:函数
为
上的凸函数.(注:
)
![](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/4562f3225c98cf5cb11b47d98c9cc9c3.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/c4b3dce3b2dd078fdd6b4cfd301927f3.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/3b0c0214295e38221c4e98d13a8b6b37.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/4776c85b79df196f606d3ebf3697fbc3.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/8ce7ae90d808f05e86ea063238e4b2f9.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/c1bedaf3854b48806b82b3b804451cf8.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/fb2d0d76b383beb0f422ed02a2b888b8.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/b6a24198bd04c29321ae5dc5a28fe421.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/4fe7d5809da02c15a43a0e9a898b9086.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/b6a24198bd04c29321ae5dc5a28fe421.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/c83590c4a7ea5636843dd4b60c67cb40.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/8ae7a1a59fbb460ff17c32dc7e3bb4ed.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/73223617c8855826298d435673787a94.png)
(1)若函数
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/9165c6db50a97f8ed52b759e57ba2644.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/a43b2faa4f81f32d94612dce724e772b.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/0a6936d370d6a238a608ca56f87198de.png)
(2)在
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/15c0dbe3c080c4c4636c64803e5c1f76.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/82822f0c261ac2193ef264fe68321833.png)
(3)若连续函数
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/be1ce3f01e2b6364f9a9fdaf197d5e29.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/870ebc2f7aabb028024894568d749934.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/ea9484fcea82180e9886a18d7a947b03.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/963c40a0a3722b8f432ee37eef7cb1a9.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/aa06f4df6281bd147ce5bd8332cfb66e.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/870ebc2f7aabb028024894568d749934.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/e56b9605ab2765c9811e9432e38d905e.png)
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