解题方法
1 . 已知各项都为正数的等比数列
满足
是
与
的等差中项,且
.
(Ⅰ)求数列
的通项公式;
(Ⅱ)设
,且
为数列
的前
项和,求数列的
的前
项和
.
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/d737c1047a14cee12a6671383e244fa5.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/20071a42c1f9eac2b173d77d37381da9.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/7755b0ec8df40da1e10c3567e441be7f.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/05b2667a6c91b720ca9b42d092c776cf.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/5b383cfc5db0978ed3869f458d538971.png)
(Ⅰ)求数列
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/d737c1047a14cee12a6671383e244fa5.png)
(Ⅱ)设
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/b83de9a45d9b680da8835bac1fee9c9b.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/08eb71ecf8d733b6932f4680874dbbf3.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/a89d1f32c1605cfdb8e8855051b9f6ec.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/b6a24198bd04c29321ae5dc5a28fe421.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/7896a1869be725f88115a74883f210e8.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/b6a24198bd04c29321ae5dc5a28fe421.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/f1ae9a3b0b7aeb1545b65d91aa371b3c.png)
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2 . 已知数列
的前
项和
.
(1)求数列
的通项公式;
(2)设
,求数列
的前
项和.
![](https://img.xkw.com/dksih/QBM/2015/11/12/1572286717435904/1572286722990080/STEM/4aecb548eb03457ebf73627a68ef2e14.png)
![](https://img.xkw.com/dksih/QBM/2015/11/12/1572286717435904/1572286722990080/STEM/9e4b482c9da3444d810737410d92916d.png)
![](https://img.xkw.com/dksih/QBM/2015/11/12/1572286717435904/1572286722990080/STEM/908defe5e2f74f6c8ed4f336c8fdb0c3.png)
(1)求数列
![](https://img.xkw.com/dksih/QBM/2015/11/12/1572286717435904/1572286722990080/STEM/f7547b586e8d4a2c94b836952218d65f.png)
(2)设
![](https://img.xkw.com/dksih/QBM/2015/11/12/1572286717435904/1572286722990080/STEM/e93d026077e64c94a3c8bde1d5fd45b7.png)
![](https://img.xkw.com/dksih/QBM/2015/11/12/1572286717435904/1572286722990080/STEM/28514fc615fb48abadb5694b5bff771b.png)
![](https://img.xkw.com/dksih/QBM/2015/11/12/1572286717435904/1572286722990080/STEM/9e4b482c9da3444d810737410d92916d.png)
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2014·河北邯郸·二模
3 . 已知等比数列前
项和为
,若
,
,则![](https://img.xkw.com/dksih/QBM/2015/11/6/1572280754692096/1572280760287232/STEM/1b9d21ad25294cb5b6b47400613acbfc.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/b6a24198bd04c29321ae5dc5a28fe421.png)
![](https://img.xkw.com/dksih/QBM/2015/11/6/1572280754692096/1572280760287232/STEM/fe6d6acea69b4e9c90e00ef6fbf09bbe.png)
![](https://img.xkw.com/dksih/QBM/2015/11/6/1572280754692096/1572280760287232/STEM/38a154b4f90f49768498d2cfdc2ae6b0.png)
![](https://img.xkw.com/dksih/QBM/2015/11/6/1572280754692096/1572280760287232/STEM/eef078fb6ff34f5380124751a4249ab1.png)
![](https://img.xkw.com/dksih/QBM/2015/11/6/1572280754692096/1572280760287232/STEM/1b9d21ad25294cb5b6b47400613acbfc.png)
A.![]() | B.![]() | C.![]() | D.![]() |
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10-11高一下·云南德宏·期中
4 . 等差数列{an}中,a2+a6=8,a3+a4=3,那么它的公差是
A.4 | B.5 | C.6 | D.7 |
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名校
5 . 等差数列{an}中,d=-2,a1+a4+a7+…+a31=50,那么a2+a6+a10+…+a42的值为( )
A.60 | B.-82 | C.182 | D.-96 |
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10-11高一下·黑龙江鹤岗·期中
名校
6 . 已知
是等比数列,
,则公比
=
![](https://img.xkw.com/dksih/QBM/2015/3/27/1572043989884928/1572043995078656/STEM/c8d5c37cf3974c7e9eb7b27aee4188b2.png)
![](https://img.xkw.com/dksih/QBM/2015/3/27/1572043989884928/1572043995078656/STEM/7bf9082f81d94769a32e23c57be6ee82.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/9aa8a716a31b0f51b70fdf9bdb257909.png)
A.![]() | B.![]() | C.2 | D.![]() |
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7 . 设等比数列
的公比
,前
项和为
,则![](https://img.xkw.com/dksih/QBM/2015/10/20/1572259713720320/1572259719553024/STEM/4b64a96e68d74832902f9b65b5873d63.png)
![](https://img.xkw.com/dksih/QBM/2015/10/20/1572259713720320/1572259719553024/STEM/064351fe78104597b11308dbf1c867e0.png)
![](https://img.xkw.com/dksih/QBM/2015/10/20/1572259713720320/1572259719553024/STEM/8611bad959fd47d1b14818bb69318ca0.png)
![](https://img.xkw.com/dksih/QBM/2015/10/20/1572259713720320/1572259719553024/STEM/075070b940af496f875f90f8ac1c3792.png)
![](https://img.xkw.com/dksih/QBM/2015/10/20/1572259713720320/1572259719553024/STEM/1310d3c018a24a39b30835e1b04d145c.png)
![](https://img.xkw.com/dksih/QBM/2015/10/20/1572259713720320/1572259719553024/STEM/4b64a96e68d74832902f9b65b5873d63.png)
A.5 | B.7 | C.8 | D.15 |
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8 . 在单调递减等比数列
中,若
则![](https://img.xkw.com/dksih/QBM/2016/1/11/1572426830594048/1572426836361216/STEM/6a204d82167e4d988a7a035afcff5615.png)
![](https://img.xkw.com/dksih/QBM/2016/1/11/1572426830594048/1572426836361216/STEM/6dcf0e458b334fe3b140e012758f033a.png)
![](https://img.xkw.com/dksih/QBM/2016/1/11/1572426830594048/1572426836361216/STEM/e1e1ef15ad84441ebf41684f350bd97c.png)
![](https://img.xkw.com/dksih/QBM/2016/1/11/1572426830594048/1572426836361216/STEM/6a204d82167e4d988a7a035afcff5615.png)
A.2 | B.4 | C.![]() | D.![]() |
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14-15高二上·河北邯郸·期末
9 . 在等差数列
中,若
,
,则公差
等于
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/83cf38189d5cbf627d2b82ac0eb76006.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/95cdd44567fe9eefb8ee7ac1d74e57ab.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/d41dae7ce63dfae1b23f7c39b142cbef.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/5c02bc0c74292b1e8f395f90935d3174.png)
A.1 | B.2 | C.3 | D.4 |
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10 . 等差数列
和
的前
项的和分别为
和
,对一切自然数
都有
,则![](https://img.xkw.com/dksih/QBM/2015/9/25/1572239647719424/1572239653535744/STEM/db1fb1981c354827a3642a921109e309.png)
![](https://img.xkw.com/dksih/QBM/2015/9/25/1572239647719424/1572239653535744/STEM/2d5dc1b2ea69472c8f502dce0a0e615f.png)
![](https://img.xkw.com/dksih/QBM/2015/9/25/1572239647719424/1572239653535744/STEM/5ca7cde99f5c41cab5fa49e1a1179d40.png)
![](https://img.xkw.com/dksih/QBM/2015/9/25/1572239647719424/1572239653535744/STEM/6afdc46dc69440b788e36349e9be9360.png)
![](https://img.xkw.com/dksih/QBM/2015/9/25/1572239647719424/1572239653535744/STEM/27b8ef54f66942a99f6d5c6488e66e13.png)
![](https://img.xkw.com/dksih/QBM/2015/9/25/1572239647719424/1572239653535744/STEM/3926c662e2cb447b96a35f990605b3aa.png)
![](https://img.xkw.com/dksih/QBM/2015/9/25/1572239647719424/1572239653535744/STEM/6afdc46dc69440b788e36349e9be9360.png)
![](https://img.xkw.com/dksih/QBM/2015/9/25/1572239647719424/1572239653535744/STEM/d45bc4072edc49498c4fc43fa8827aad.png)
![](https://img.xkw.com/dksih/QBM/2015/9/25/1572239647719424/1572239653535744/STEM/db1fb1981c354827a3642a921109e309.png)
A.![]() | B.![]() | C.![]() | D.![]() |
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