23-24高二下·全国·课前预习
1 . 等差数列的前
项和公式
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/b6a24198bd04c29321ae5dc5a28fe421.png)
已知量 | 首项、末项与项数 | 首项、公差与项数 |
求和公式 | ![]() | ![]() |
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23-24高二下·全国·课前预习
解题方法
2 . 等差数列前
项和的性质
(1)若数列
是公差为
的等差数列,则数列
也是等差数列,且公差为______ .
(2)若
分别为等差数列
的前
项,前
项,前
项的和,则
,
也成等差数列,公差为______ .
(3)设两个等差数列
的前
项和分别为
,则![](https://staticzujuan.xkw.com/quesimg/Upload/formula/a6322378e9dc138599481f035cfe3b38.png)
______ .
(4)在等差数列中,若
,则![](https://staticzujuan.xkw.com/quesimg/Upload/formula/be2e0d4d2e550f00b36d6f00111418ba.png)
______ .
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/b6a24198bd04c29321ae5dc5a28fe421.png)
(1)若数列
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/83cf38189d5cbf627d2b82ac0eb76006.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/5c02bc0c74292b1e8f395f90935d3174.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/4dea1dd4ffcb4cf0697ca43079f6a1f2.png)
(2)若
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/35ddff98f658432f3723f43951abd46e.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/83cf38189d5cbf627d2b82ac0eb76006.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/294f5ba74cdf695fc9a8a8e52f421328.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/fad491e5b5e14c49ef8b7004ebcfcef9.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/ade9841a8e6840efddcfd8620a6fc1fd.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/6b477afc102fe376cc777fffe0548cb0.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/aacaf4a1b543085ebf2617cd600c011a.png)
(3)设两个等差数列
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/62e567d7e9761951a266953c8d5042ac.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/b6a24198bd04c29321ae5dc5a28fe421.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/478421b81927e435cbcf5acafa89efd7.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/a6322378e9dc138599481f035cfe3b38.png)
(4)在等差数列中,若
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/2bcbc6ca5f2b222970ce2473603d54b8.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/be2e0d4d2e550f00b36d6f00111418ba.png)
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2023高二·全国·专题练习
解题方法
3 . 等差数列的通项公式与前n项和公式
(1)通项公式:![](https://staticzujuan.xkw.com/quesimg/Upload/formula/e3f7fda69e2b32b9ced2239f915fa59b.png)
________ . 该式又可以写成![](https://staticzujuan.xkw.com/quesimg/Upload/formula/e3f7fda69e2b32b9ced2239f915fa59b.png)
__________ ,这表明d≠0时,
是关于n的一次函数,且d>0时是增函数,d<0时是减函数.
(2)前n项和公式:![](https://staticzujuan.xkw.com/quesimg/Upload/formula/04c2864e2ec3416cc4c081ac1f71a0af.png)
__________ =___________ . 该式又可以写成![](https://staticzujuan.xkw.com/quesimg/Upload/formula/04c2864e2ec3416cc4c081ac1f71a0af.png)
___________ ,这表明d≠0时,
是关于n的二次函数,且d>0时图象开口向上,d<0时图象开口向下.
(1)通项公式:
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/e3f7fda69e2b32b9ced2239f915fa59b.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/e3f7fda69e2b32b9ced2239f915fa59b.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/96abfe2da27a63e6affb19a0c80236d9.png)
(2)前n项和公式:
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/04c2864e2ec3416cc4c081ac1f71a0af.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/04c2864e2ec3416cc4c081ac1f71a0af.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/08eb71ecf8d733b6932f4680874dbbf3.png)
您最近一年使用:0次