等差数列
、
、
、
的第五项等于( )
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/bdaa19de263700a15fcf213d64a8cd57.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/878e89b6eca35e34c863e832a2c661db.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/4d1f948f90d6b533032351ee44289931.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/daa5e9bd516f6282483b92cfe6074623.png)
A.![]() | B.![]() | C.![]() | D.![]() |
2021·海南·模拟预测 查看更多[2]
更新时间:2021-05-07 17:10:57
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【推荐1】等差数列{an}的公差为2,若a2,a4,a8成等比数列,则{an}的通项an=( )
A.n﹣1 | B.2n | C.2n﹣1 | D.2n+1 |
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【推荐2】等差数列
的前
项和为
,若
,且
,则
( )
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/83cf38189d5cbf627d2b82ac0eb76006.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/b6a24198bd04c29321ae5dc5a28fe421.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/08eb71ecf8d733b6932f4680874dbbf3.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/939239eca344c1a9d4b232a34a48ca1a.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/c46cb0c7c9e66575cfd70a6aba22c280.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/dd707b69a11f8de5566f23c1a2a9ff5a.png)
A.10 | B.7 | C.12 | D.3 |
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解题方法
【推荐1】在
中,若
,
,
成等差数列,且
,
,则![](https://staticzujuan.xkw.com/quesimg/Upload/formula/c5f1e5d29de6e4d72bfed62d9c14dde5.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/0faed94a64b2dcfc6801b4fca0f16675.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/5963abe8f421bd99a2aaa94831a951e9.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/7f9e8449aad35c5d840a3395ea86df6d.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/c5db41a1f31d6baee7c69990811edb9f.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/10c013bbe1fb6e9acf461548b5cf6cd2.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/ef0402dd5ae3db10281f9f1e11738bcb.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/c5f1e5d29de6e4d72bfed62d9c14dde5.png)
A.![]() | B.![]() | C.![]() | D.![]() ![]() |
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【推荐2】若
是等差数列,
与
的等差中项为1,
与
的等差中项为2,则公差![](https://staticzujuan.xkw.com/quesimg/Upload/formula/a72a51e6b20553396fd2351e7e712414.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/63d471926f7b27322d90c82b9ce21d3d.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/e72adb45c60c2f63b46e65ff787302bf.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/3e88093a749c0d46e0ee931ecfaff925.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/3e88093a749c0d46e0ee931ecfaff925.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/6c1ccc6c74b8754e9bcbb3f39a11b6f1.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/a72a51e6b20553396fd2351e7e712414.png)
A.1 | B.2 | C.![]() | D.![]() |
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