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
2 . 等差数列的概念
(1)“从第2项起”是指第1项前面没有项,无法与后续条件中“与前一项的差”相吻合;(2)“每一项与它的前一项的差”这一运算要求是指“相邻且后项减去前项”,强调了:
①.作差的顺序;
②.这两项必须相邻;
(3)定义中的“同一常数”是指全部的后项减去前一项都等于同一个常数,否则这个数列不能称为等差数列.
条件 | 从第 |
每一项与它的 | |
结论 | 这个数列就叫做等差数列 |
有关概念 | 这个常数叫做等差数列的 |
①.作差的顺序;
②.这两项必须相邻;
(3)定义中的“同一常数”是指全部的后项减去前一项都等于同一个常数,否则这个数列不能称为等差数列.
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23-24高二下·全国·课前预习
3 . 等差数列两项或多项之间的性质
是公差为
的等差数列,若正整数
满足
,则
________
(1)特别地,当
时,
.
(2)对有穷等差数列,与首末两项“等距离”的两项之和等于首末两项的和,即
![](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/0e29257946a2508fcd5fe8d1b01fa139.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/4fb679318d0c9819b82e51a1750b502a.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/ba762a8f28fb54819203249c265e679a.png)
(1)特别地,当
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/0106f37761a1af47d6e47ca05212b62c.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/3993a361182c983859ca4f752521de12.png)
(2)对有穷等差数列,与首末两项“等距离”的两项之和等于首末两项的和,即
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/95caa06d35c8d8bc383487ee9620db5d.png)
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23-24高二下·全国·课前预习
4 . 等差数列通项公式的变形及推广
(1)
,
(2)![](https://staticzujuan.xkw.com/quesimg/Upload/formula/2a26b10d182d3b41ff05beea6edfdf18.png)
________ ![](https://staticzujuan.xkw.com/quesimg/Upload/formula/69421e5e6e1f03af5335ea0faa077de9.png)
(3)![](https://staticzujuan.xkw.com/quesimg/Upload/formula/7c98c59cd4749afdd21e73529fc84323.png)
________
,且
.
(1)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/65287b4936b1d642651ec534faee79ad.png)
(2)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/2a26b10d182d3b41ff05beea6edfdf18.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/69421e5e6e1f03af5335ea0faa077de9.png)
(3)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/7c98c59cd4749afdd21e73529fc84323.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/02ac5b6cc698996f7aac77a0d75d02d4.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/abb55a6ac710d45ef73be9d94340f7df.png)
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23-24高二下·全国·课前预习
5 . 由等差数列构造新等差数列
(1)若
分别是公差为
的等差数列,则有
(2)从等差数列中,每隔一定的距离抽取一项,组成的数列仍为________ 数列.
(1)若
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/ed48c3e5c53eba20c2e262b7d2c09bfc.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/fd14c565598848a980c4050c882812bd.png)
数列 | 结论 |
![]() | 公差为![]() |
![]() | 公差为![]() |
![]() | 公差为![]() ![]() |
![]() | 公差为![]() |
(2)从等差数列中,每隔一定的距离抽取一项,组成的数列仍为
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23-24高二下·全国·课前预习
6 . 等差数列的通项公式
首项为
,公差为
的等差数列
的通项公式是![](https://staticzujuan.xkw.com/quesimg/Upload/formula/e3f7fda69e2b32b9ced2239f915fa59b.png)
________
温馨提醒
(1)由等差数列的通项公式可以求出该数列中的任意项,也可以判断某一个数是不是该数列中的项;
(2)根据等差数列的两个已知条件建立关于“基本量”
和
的方程组,求出
和
,从而确定通项公式,求得所需求的项.
首项为
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/e72adb45c60c2f63b46e65ff787302bf.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/5c02bc0c74292b1e8f395f90935d3174.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/83cf38189d5cbf627d2b82ac0eb76006.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/e3f7fda69e2b32b9ced2239f915fa59b.png)
温馨提醒
(1)由等差数列的通项公式可以求出该数列中的任意项,也可以判断某一个数是不是该数列中的项;
(2)根据等差数列的两个已知条件建立关于“基本量”
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/e72adb45c60c2f63b46e65ff787302bf.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/5c02bc0c74292b1e8f395f90935d3174.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/e72adb45c60c2f63b46e65ff787302bf.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/5c02bc0c74292b1e8f395f90935d3174.png)
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23-24高二下·全国·课前预习
7 . 等差中项
(1)条件:如果
成等差数列.
(2)结论:那么
叫做
与
的等差中项.
(3)满足的关系式是________
温警提醒(1)任意两个实数都有等差中项.
(2)应用等差中项法也可证明一个数列为等差数列,即
为等差数列.
(1)条件:如果
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/5bf6726a4207c053c937cf221120dea1.png)
(2)结论:那么
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/5963abe8f421bd99a2aaa94831a951e9.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/0a6936d370d6a238a608ca56f87198de.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/2c94bb12cee76221e13f9ef955b0aab1.png)
(3)满足的关系式是
温警提醒(1)任意两个实数都有等差中项.
(2)应用等差中项法也可证明一个数列为等差数列,即
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/1aa511f5869c3ac911876fc9af0f51b1.png)
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23-24高二下·全国·课前预习
解题方法
8 . 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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23-24高二下·全国·课前预习
解题方法
9 . 已知等差数列
的前
项和为
,且
,
,则
( )
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/5da32e6c01e47e8c84a7ff44ac125a5a.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/b6a24198bd04c29321ae5dc5a28fe421.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/70cb7b6d14630288595af4d9ad841312.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/8ad088f3ec8297e74e50a01e5e76b0cc.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/e2a55aadc0a7cd1b97eced4e34793f5e.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/5af1f1b7e9e20d799ee3c06b89a0611c.png)
A.![]() | B.![]() | C.![]() | D.![]() |
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23-24高二下·全国·课前预习
解题方法
10 . 已知{an}满足
,
,则
的值为( )
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/8323901a49cac29afd7d62864f088077.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/424edbd0bfe737cbb80c87d3c17ff560.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/4c4775666a3fd90a5623efeac883aeec.png)
A.48 | B.96 |
C.120 | D.130 |
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