23-24高二下·全国·课前预习
1 . 知识点03等比数列的单调性
等比数列
的首项为
,公比为![](https://staticzujuan.xkw.com/quesimg/Upload/formula/9aa8a716a31b0f51b70fdf9bdb257909.png)
(1)当___ 时,数列为递增数列;
(2)当___ 时,数列为递减数列;
(3)当_____ 时,数列为常数列:
(4)当_______ 时,数列为摆动数列.
等比数列
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/29518f13a1ebc3fff8181c2d7cfba22f.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/1b42791b77924729f7e31712177b26af.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/9aa8a716a31b0f51b70fdf9bdb257909.png)
(1)当
(2)当
(3)当
(4)当
您最近一年使用:0次
23-24高二下·全国·课前预习
2 . 知识点01等比数列的概念
1、等比数列的定义
如果一个数列从第2项起,_______ 等于同一常数,那么这个数列叫做等比数列,这个常数叫做等比数列的_______ ,通常用字母_______ 表示
.
2、对等比数列概念的理解
(1)“从第2项起”,是因为首项没有“前一项”,同时注意公比是每一项与前一项的比,前后次序不能颠倒,另外等比数列中至少含有三项;
(2)定义中的“同一常数”是定义的核心之一,一定不能把“同”字省略,这是因为如果一个数列从第2项起,每一项与它的前一项的比都是一个与
无关的常数,但是如果这些常数不相同,那么此数列也不是等比数列,当且仅当这些常数相同时,数列才是等比数列;
(3)若一个数列不是从第2项起,而是从第3项起或第
项起,每一项与它的前一项的比等于同一常数,则此数列不是等比数列;
(4)由定义可知,等比数列的任一项都不为0,且公比
;
(5)不为0的常数列是特殊的等比数列,其公比为1.
1、等比数列的定义
如果一个数列从第2项起,
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/455931a43e525371730e61177c48aec6.png)
2、对等比数列概念的理解
(1)“从第2项起”,是因为首项没有“前一项”,同时注意公比是每一项与前一项的比,前后次序不能颠倒,另外等比数列中至少含有三项;
(2)定义中的“同一常数”是定义的核心之一,一定不能把“同”字省略,这是因为如果一个数列从第2项起,每一项与它的前一项的比都是一个与
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/b6a24198bd04c29321ae5dc5a28fe421.png)
(3)若一个数列不是从第2项起,而是从第3项起或第
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/bccd5c35461ea19c93e24f80e8538f2d.png)
(4)由定义可知,等比数列的任一项都不为0,且公比
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/0a3ac83c571110d41a396d12d8eea1c6.png)
(5)不为0的常数列是特殊的等比数列,其公比为1.
您最近一年使用:0次
23-24高二下·全国·课前预习
3 . 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
您最近一年使用:0次
23-24高二下·全国·课前预习
4 . 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)
您最近一年使用:0次
23-24高二下·全国·课前预习
5 . 知识点05等比数列的性质
1、“子数列”性质
(1)对于无穷等比数列
,若将其前
项去掉,剩余各项仍为等比数列,首项为
,公比为
;
若取出所有的
的倍数项,组成的数列仍为等比数列,首项为
,公比为
;
(2)相隔等距离的项组成的数列仍是等比数列,即
仍是等比数列,公比为 ____ ![](https://staticzujuan.xkw.com/quesimg/Upload/formula/c7ee88f532329c9fbc70d6c544497292.png)
2、“下标和”性质:在等比数列
中,若
,则____ ;
(1)特别地,
时,____ ;
当
时,____
(2)若数列
是有穷数列,则与首末两项“等距离”的两项的积等于首末两项的积,即![](https://staticzujuan.xkw.com/quesimg/Upload/formula/e4ddaf21329cb1824329c296eaad5336.png)
3、两等比数列合成数列的性质:若数列
是项数相同的等比数列,
是不等于0的常数,则数列
也是____ .
1、“子数列”性质
(1)对于无穷等比数列
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/83cf38189d5cbf627d2b82ac0eb76006.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/f0a532e15e232cb4b99a8d4d07c89575.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/217b927efe12a98e1082ecd7f035b921.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/9aa8a716a31b0f51b70fdf9bdb257909.png)
若取出所有的
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/f0a532e15e232cb4b99a8d4d07c89575.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/5f255d0395fba51ca2d44293cca42e0a.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/e248261e3017741f15614caea31d0ce0.png)
(2)相隔等距离的项组成的数列仍是等比数列,即
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/7b7802fa4893785d5a8f6ea1edb8cffe.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/c7ee88f532329c9fbc70d6c544497292.png)
2、“下标和”性质:在等比数列
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/83cf38189d5cbf627d2b82ac0eb76006.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/23f0c04bf4f330778a67c31371c5cf64.png)
(1)特别地,
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/d35a47bf120bdc9294da261220947532.png)
当
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/865b6be02589dde9a2fb834ee7b8004b.png)
(2)若数列
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/83cf38189d5cbf627d2b82ac0eb76006.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/e4ddaf21329cb1824329c296eaad5336.png)
3、两等比数列合成数列的性质:若数列
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/ed48c3e5c53eba20c2e262b7d2c09bfc.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/071a7e733d466949ac935b4b8ee8d183.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/50e60f14235ca70ecc310820a747a548.png)
您最近一年使用:0次
23-24高二下·全国·课前预习
6 . 等比数列前
项和公式的函数特征
(1)当公比
时,设
,等比数列的前
项和公式是
,即
是
的________ (2)当公比
时,因为
,所以
是
的________ .
温馨提醒:当
,所以
的结构形式.
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/b6a24198bd04c29321ae5dc5a28fe421.png)
(1)当公比
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/45482d31d1d7448c9f3922b4d2a55331.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/c9eb685890a92dfb9abf497f6a28d1c7.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/b6a24198bd04c29321ae5dc5a28fe421.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/5d7eacf0e45686808894857edcfddcd6.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/08eb71ecf8d733b6932f4680874dbbf3.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/b6a24198bd04c29321ae5dc5a28fe421.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/dfa9bf65189dfb57a61644a1cb27f361.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/fc9efeb4455e30293d412938eeea85d5.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/e9285e2558a49fd5b378dde4878ac346.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/b6a24198bd04c29321ae5dc5a28fe421.png)
温馨提醒:当
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/c81333addf3c81ac7ea2341e513d5308.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/c94cdb9f5e337d904ed26230e2406291.png)
您最近一年使用:0次
23-24高二下·全国·课前预习
7 . 等比数列的前
项和公式
注:用等比数列前
项和公式求和,一定要对该数列的公比________ ,进行分类讨论;
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/b6a24198bd04c29321ae5dc5a28fe421.png)
已知量 | 首项、公比和项数 | 首项、末项和公比 |
公式 | ![]() | ![]() |
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/b6a24198bd04c29321ae5dc5a28fe421.png)
您最近一年使用:0次
8 . 等比数列的前
项和
已知
为等比数列且公比为
,
为其前
项和.
(1)![](https://staticzujuan.xkw.com/quesimg/Upload/formula/61b7a07ade5913a6e6b54dbf1c23a5f3.png)
________ 或者![](https://staticzujuan.xkw.com/quesimg/Upload/formula/8d0980e3f744e203ae45c4bbb442e336.png)
________
(2)我们用方法________ 推导
.
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/b6a24198bd04c29321ae5dc5a28fe421.png)
已知
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/83cf38189d5cbf627d2b82ac0eb76006.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/9aa8a716a31b0f51b70fdf9bdb257909.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/08eb71ecf8d733b6932f4680874dbbf3.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/b6a24198bd04c29321ae5dc5a28fe421.png)
(1)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/61b7a07ade5913a6e6b54dbf1c23a5f3.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/8d0980e3f744e203ae45c4bbb442e336.png)
(2)我们用方法
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/08eb71ecf8d733b6932f4680874dbbf3.png)
您最近一年使用:0次
9 . 等比数列的性质
已知
为等比数列,公比为
,
为其前
项和.
(1)若
,则![](https://staticzujuan.xkw.com/quesimg/Upload/formula/8647b84bfbc7d827f56be74888b9fdb6.png)
______ ;
(2)当
时,
,________ ,
为等比数列;
(3)若等比数列
共
项,记
为诸奇数项和,
为诸偶数项和,则![](https://staticzujuan.xkw.com/quesimg/Upload/formula/186fad5c3b123434e46e02c26dcc3c32.png)
____ ;
已知
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/83cf38189d5cbf627d2b82ac0eb76006.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/9aa8a716a31b0f51b70fdf9bdb257909.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/08eb71ecf8d733b6932f4680874dbbf3.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/b6a24198bd04c29321ae5dc5a28fe421.png)
(1)若
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/c618d7069d2e18c8164ed0e6fa7811f0.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/8647b84bfbc7d827f56be74888b9fdb6.png)
(2)当
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/f1d236a265a6cc0f3d06a0e568ffa907.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/08eb71ecf8d733b6932f4680874dbbf3.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/b7ce01c8a13621ad26ea353b067dfaa8.png)
(3)若等比数列
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/83cf38189d5cbf627d2b82ac0eb76006.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/8b5631bc01b998a4b3fabd9e131699dc.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/9df956d8d43778655131703be9ad9a41.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/16ce99d82b6ad34142c6920031a454e9.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/186fad5c3b123434e46e02c26dcc3c32.png)
您最近一年使用:0次
10 . 等比数列的前
项和
已知
为等比数列且公比为
,
为其前
项和.
(1)![](https://staticzujuan.xkw.com/quesimg/Upload/formula/04c2864e2ec3416cc4c081ac1f71a0af.png)
____________ 或者![](https://staticzujuan.xkw.com/quesimg/Upload/formula/04c2864e2ec3416cc4c081ac1f71a0af.png)
___________ .
(2)我们用方法_______________ 推导
.
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/b6a24198bd04c29321ae5dc5a28fe421.png)
已知
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/83cf38189d5cbf627d2b82ac0eb76006.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/9aa8a716a31b0f51b70fdf9bdb257909.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/08eb71ecf8d733b6932f4680874dbbf3.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/b6a24198bd04c29321ae5dc5a28fe421.png)
(1)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/04c2864e2ec3416cc4c081ac1f71a0af.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/04c2864e2ec3416cc4c081ac1f71a0af.png)
(2)我们用方法
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/08eb71ecf8d733b6932f4680874dbbf3.png)
您最近一年使用:0次