23-24高二下·全国·课前预习
1 . 知识点04等比中项
1、等比中项定义:如果在
与
中间插入一个数
,使
成等比数列,那么
叫做
与
的_______ ,即
是
与
的等比中项
成等比数列![](https://staticzujuan.xkw.com/quesimg/Upload/formula/f39c662a3927de39135c3eee4b9cb68f.png)
_______
2、对等比中项概念的理解
(1)
是
与
的等比中项,则
与
的符号相同,符号相反的两个实数不存在等比中项.此时,
,即等比中项有两个,且互为相反数.
(2)
时,![](https://staticzujuan.xkw.com/quesimg/Upload/formula/895dc3dc3a6606ff487a4c4863e18509.png)
_______ 是
与
的等比中项.例如
,但
不是等比数列;
(3)在等比数列
中,从第2项起,每一项是它相邻两项的等比中项;
(4)与等比数列中的任一项“等距离”的两项之积等于该项的平方,即在等比数列
中,![](https://staticzujuan.xkw.com/quesimg/Upload/formula/6a6169cb2b9f2a373abc0cadecadd4f2.png)
3、等差中项与等比中项区别
(1)任意两数都存在等差中项,但并不是任意两数都存在等比中项,当且仅当两数同号且均不为0时才存在等比中项;
(2)任意两数的等差中项是______ 的,而若两数有等比中项,则等比中项______ .
1、等比中项定义:如果在
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/0a6936d370d6a238a608ca56f87198de.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/2c94bb12cee76221e13f9ef955b0aab1.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/895dc3dc3a6606ff487a4c4863e18509.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/e6703df340de9d28c32832badbd30f22.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/895dc3dc3a6606ff487a4c4863e18509.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/0a6936d370d6a238a608ca56f87198de.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/2c94bb12cee76221e13f9ef955b0aab1.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/895dc3dc3a6606ff487a4c4863e18509.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/0a6936d370d6a238a608ca56f87198de.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/2c94bb12cee76221e13f9ef955b0aab1.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/83ab5539817e40ffaf20a517e0978b80.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/f39c662a3927de39135c3eee4b9cb68f.png)
2、对等比中项概念的理解
(1)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/895dc3dc3a6606ff487a4c4863e18509.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/0a6936d370d6a238a608ca56f87198de.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/2c94bb12cee76221e13f9ef955b0aab1.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/0a6936d370d6a238a608ca56f87198de.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/2c94bb12cee76221e13f9ef955b0aab1.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/ede7e2c31ca68ce700cffa87764dc484.png)
(2)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/a1c8379fe535e68721fd84be969d257f.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/895dc3dc3a6606ff487a4c4863e18509.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/0a6936d370d6a238a608ca56f87198de.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/2c94bb12cee76221e13f9ef955b0aab1.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/9ce438ef49c36ad7b8a27e918137e9ab.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/419abd403ca442c5aadd04165fc9a528.png)
(3)在等比数列
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/83cf38189d5cbf627d2b82ac0eb76006.png)
(4)与等比数列中的任一项“等距离”的两项之积等于该项的平方,即在等比数列
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/83cf38189d5cbf627d2b82ac0eb76006.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/6a6169cb2b9f2a373abc0cadecadd4f2.png)
3、等差中项与等比中项区别
(1)任意两数都存在等差中项,但并不是任意两数都存在等比中项,当且仅当两数同号且均不为0时才存在等比中项;
(2)任意两数的等差中项是
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23-24高二下·全国·课前预习
2 . 知识点02等比数列的通项公式及其推广
1、等比数列的通项公式:等比数列
的首项为
,公比为
,则通项公式为:
_______
2、通项公式的推广:![](https://staticzujuan.xkw.com/quesimg/Upload/formula/e3f7fda69e2b32b9ced2239f915fa59b.png)
______ 或
______
1、等比数列的通项公式:等比数列
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/76aef4cdcb5af742ce28003b7b6c8c20.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/e72adb45c60c2f63b46e65ff787302bf.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/c2815c76b21860c4a2af5be1e3023a48.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/e3f7fda69e2b32b9ced2239f915fa59b.png)
2、通项公式的推广:
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/e3f7fda69e2b32b9ced2239f915fa59b.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/85a34cc0abc5c3b4f646d907f6b5e314.png)
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23-24高二下·全国·课前预习
3 . 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
4 . 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
5 . 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
6 . 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
7 . 错位相减法
(1)推导等比数列前
项和的方法叫________ ;
(2)该方法一般适用于求________ 的前
项和,即若
是公差
的等差数列,
是公比
的等比数列,求数列
的前
项和
时,可以用这种方法.
(1)推导等比数列前
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/b6a24198bd04c29321ae5dc5a28fe421.png)
(2)该方法一般适用于求
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/b6a24198bd04c29321ae5dc5a28fe421.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/034ba25825c13725931c483aa47c9363.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/812be9806122241c476ba1db516c4823.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/57ef6d44448092ebdb9e4a49d866a749.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/45482d31d1d7448c9f3922b4d2a55331.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/c19a6a8737d38c958d1443a7414e237f.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/b6a24198bd04c29321ae5dc5a28fe421.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/08eb71ecf8d733b6932f4680874dbbf3.png)
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23-24高二下·全国·课前预习
8 . 数学归纳法的操作流程
(1)________ 奠基要稳,有些问题中验证的初始值
不一定为1.
(2)正确分析由
到
时式子________ 是应用数学归纳法成功证明问题的保障.
(3)在第二步证明中一定要________ ,这是数学归纳法证明的核心环节,否则这样的证明就不是利用数学归纳法证明.
(1)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/16530bfffc3b0bb4bda872bf43a3b82f.png)
(2)正确分析由
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/f2b66d04abdc608824821dee4c842065.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/3e8d70d8c5c609c5b55dd2d795be9648.png)
(3)在第二步证明中一定要
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23-24高一下·全国·课前预习
9 . 两个复数相乘时,如图所示,先画出与
对应的向量
,
,然后把向量
绕点
按_____ 时针方向旋转角
,(如果
,就要把
绕点
按_____ 时针方向旋转
),再把它的模变为原来的____ 倍,得到向量
,
表示的复数就是积_____ ,这是复数乘法的几何意义.
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/90d860cb86e1467ac24010aecfc7a425.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/a30deb1f343048675b9b231620369668.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/a1640d3fff861f45c5eb4019943b000f.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/a30deb1f343048675b9b231620369668.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/1dde8112e8eb968fd042418dd632759e.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/e93fa313adc4ac7608ba9449fd755212.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/d442c6f979cd09bb7f8acf01d70130fe.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/a30deb1f343048675b9b231620369668.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/1dde8112e8eb968fd042418dd632759e.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/ba62723e05ce6cce4d089d8b201fa857.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/eeb0e25bbccbee4a1b9db38b49e87978.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/eeb0e25bbccbee4a1b9db38b49e87978.png)
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