题目内容
设数列
满足
。
(1)求数列
的通项公式
;
(2)令
,求数列
的前
项和
;
。
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823211859615480.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823211859631768.png)
(1)求数列
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823211859615480.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823211859678348.png)
(2)令
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823211859693553.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823211859709487.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823211859709297.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823211859724388.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/201408232118597401867.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823211859756515.png)
(1)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/201408232118597871795.png)
(2)略
本试题主要是考查了运用递推关系式求解数列的通项公式的运用,通过累加法来完成。而第二问主要是运用分组求和来表示和式,并进行适当的放缩,证明不等式。
解:
(1)![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823211859787458.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823211859802665.png)
…………………………2分
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/201408232118598492205.png)
经验证n=1也成立。(无此扣一分)
………………………………4分
(2)![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823211859880832.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823211859880644.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823211859912650.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823211859927654.png)
…………
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823211859943691.png)
…………6分
设
①
②
①-②
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823211900068943.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/201408232119000831196.png)
……………………………………9分
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/201408232119001301264.png)
……………………10分
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/201408232119001774359.png)
解:
(1)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823211859787458.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823211859802665.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/201408232118598341184.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/201408232118598492205.png)
经验证n=1也成立。(无此扣一分)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823211859865671.png)
(2)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823211859880832.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823211859880644.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823211859912650.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823211859927654.png)
…………
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823211859943691.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/201408232118599581777.png)
设
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823211859974959.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/201408232118599901355.png)
①-②
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823211900068943.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/201408232119000831196.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823211900114734.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/201408232119001301264.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/201408232119001461083.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/201408232119001774359.png)
![](http://thumb.zyjl.cn/images/loading.gif)
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