1 . 裂项求和
把数列的通项拆成两项之差,在求和时中间的一些项可以相互抵消,从而求得前
项和.
裂项时常用的五种变形:
(1)![](https://staticzujuan.xkw.com/quesimg/Upload/formula/ac067a9b66a44acd5abaa0c021b5e3e5.png)
______
;
(2)![](https://staticzujuan.xkw.com/quesimg/Upload/formula/d06787f1848280ca6ca23d14da193321.png)
______ .
(3)![](https://staticzujuan.xkw.com/quesimg/Upload/formula/4efaa1a53624d5942626cf9bddc288d3.png)
______
;
(4)![](https://staticzujuan.xkw.com/quesimg/Upload/formula/235c44b3845afe108250918d8b41a339.png)
______ .
(5)若数列
是等差数列,且公差
,则![](https://staticzujuan.xkw.com/quesimg/Upload/formula/c0ade8d55a7d63674831f8c559ab5707.png)
______ .
把数列的通项拆成两项之差,在求和时中间的一些项可以相互抵消,从而求得前
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/b6a24198bd04c29321ae5dc5a28fe421.png)
裂项时常用的五种变形:
(1)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/ac067a9b66a44acd5abaa0c021b5e3e5.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/c3cb77304ba3546c1fc629832f1b811f.png)
(2)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/d06787f1848280ca6ca23d14da193321.png)
(3)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/4efaa1a53624d5942626cf9bddc288d3.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/c3cb77304ba3546c1fc629832f1b811f.png)
(4)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/235c44b3845afe108250918d8b41a339.png)
(5)若数列
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/83cf38189d5cbf627d2b82ac0eb76006.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/812be9806122241c476ba1db516c4823.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/c0ade8d55a7d63674831f8c559ab5707.png)
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解题方法
2 . 完成下列表格:
递推关系 | 求法 | 名称 |
![]() | ![]() | 累加 |
![]() | ![]() | 累乘 |
![]() | ![]() | 取倒数 |
![]() | ![]() | 构造法 |
![]() | 利用![]() | 转化法 |
您最近一年使用:0次