已知數(shù)列
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824032207737457.png)
的前
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824032207752277.png)
項和
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824032207768540.png)
(
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824032207768505.png)
),則
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824032207784357.png)
的值是__________.
試題分析:只要理解數(shù)列的項
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824032207799348.png)
與前
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824032207752277.png)
項和
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824032207830388.png)
的關(guān)系即可很快得解,
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824032207846860.png)
.
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824032207799348.png)
與前
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824032207752277.png)
項和
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824032207830388.png)
的關(guān)系:
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/201408240322078931073.png)
.
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