设

是正项数列

的前

项和,且

(

).
(Ⅰ)求数列

的通项公式;
(Ⅱ)若

,设

,求数列

的前

项和

.
考查数列中

之间的关系,

,可解得

的通项公式,由

得出

并做差,是关键;

是差比数列,其和用错误相减法,


相同次数对齐,注意最后一项的符号。
(Ⅰ)当

时,

,解得

(舍去),

.
当

时,由

得,

,
两式作差,得

,
整理得

,

,

,

,

数列

为正项数列,

,


,即

,数列

是公差为

的等差数列,


.
(Ⅱ)


,


,①

,②

,


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科目:高中数学
来源:不详
题型:解答题
已知各项都不为零的数列

的前n项和为

,

,向量

,其中

N
*,且

∥

.
(Ⅰ)求数列

的通项公式及

;
(Ⅱ)若数列

的前n项和为

,且

(其中

是首项

,第四项为

的等比数列的公比),求证:

.
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科目:高中数学
来源:不详
题型:解答题
设数列

的前

项和为

,且满足

,

,

.
(1)猜想

的通项公式,并加以证明;
(2)设

,且

,证明:

.
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科目:高中数学
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题型:解答题
已知

为等差数列,且

.
(1)求数列

的通项公式; (2)令

,求数列

的前

项和

.
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
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
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
}的前2012项和

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