题目内容
已知数列
的前
项和
满足
,且
.
⑴ 求
的值;
⑵ 猜想
的表达式(不必证明)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823205854108486.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823205854264297.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823205854279388.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823205854310921.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823205854326478.png)
⑴ 求
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823205854342506.png)
⑵ 猜想
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823205854357347.png)
⑴ 当
时,
,即
,
而
,因此
;……2分
当
时,
,即
,
而
,因此
;………………………………4分
同理
. ………………………………6分
⑵ 由⑴知:
,
,
,
.………………………………10分
由以上规律,可以猜测
.
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823205854388392.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823205854404542.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823205854420540.png)
而
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823205854451478.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823205854560512.png)
当
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823205854778382.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823205854810549.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823205854825605.png)
而
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823205854981696.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823205855012529.png)
同理
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823205855184551.png)
⑵ 由⑴知:
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823205855387632.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823205855465737.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823205855512732.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823205855543764.png)
由以上规律,可以猜测
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823205855558712.png)
略
![](http://thumb2018.1010pic.com/images/loading.gif)
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