(本小题满分12分)已知数列
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满足
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且
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,数列
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的前
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项和为
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。
(1)求数列
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的通项
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; (2)求
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;
(3)设
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,求证:
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≥
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。
解:(1)由
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得

,且
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,∴数列

是以2为首项,2为公比的等比数列,
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,∴
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。
(2)由(1)知
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,∴
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,
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。
(3)
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当
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时,
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;
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>
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时
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>0,
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在
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上递增;
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<
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<
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时,
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∴
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≥
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成立。
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相关习题
科目:高中数学
来源:不详
题型:解答题
(本小题满分14分)
已知数列
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是各项均不为

的等差数列,公差为
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,
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为其前
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项和,且满足
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,
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.数列
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满足

,
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为数列

的前
n项和.
(1)求
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、

和
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;
(2)若对任意的

,不等式
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恒成立,求实数
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的取值范围;
(3)是否存在正整数
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
,使得

成等比数列?若存在,求出所有
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的值;若不存在,请说明理由.
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科目:高中数学
来源:不详
题型:解答题
(本题满分10分)
已知数列
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中,
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,
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,且


.
(1)设
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,证明

是等比数列;
(2)求数列

的通项公式;
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科目:高中数学
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已知数列

满足条件

,

,

,设


(1)求数列

的通项公式;
(2)求和:

。(14分)
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来源:不详
题型:解答题
(本小题满分12分)
设数列

的各项都为正数,其前

项和为

,已知对任意

,

是
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和

的等比中项.
(Ⅰ)证明数列

为等差数列,并求数列

的通项公式;
(Ⅱ)证明

;
(Ⅲ)设集合

,

,且

,若存在

∈

,使对满足

的一切正整数

,不等式

恒成立,求这样的正整数

共有多少个?
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来源:不详
题型:解答题
设数列

满足关系式:

(
p是常数).
(Ⅰ)求

;
(Ⅱ)猜想

的通项公式,并证明.
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科目:高中数学
来源:不详
题型:解答题
设


(1)写出

的递推关系式,并求出

的通项公式;
(2)若

试比较

大小

并证明
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科目:高中数学
来源:不详
题型:填空题
数列

的通项公式为

,

达到最小时,
n等于_______________.
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