解题方法
1 . 已知等差数列
的前
项和为
,且
,
,有下列结论:
①
;②
;③
;④
.
其中正确的是______ .(填写所有正确结论的编号)
![](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/d0d47abde02e3d7ffb3484878ba43c19.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/db78d2181208520e31797e6538e1c6d8.png)
①
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/e7a47513805617d84ad1e248c5415e5b.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/42fa3df245bef16f30ef05302998bd39.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/1d8ee4c1f66f600c90d457a267aa0991.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/390636a89883bd64bf8da9bf8654aff9.png)
其中正确的是
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2 . 数学中有各式各样富含诗意的曲线,螺旋线就是其中比较特别的一类.螺旋线这个名词来源于希腊文,它的原意是“旋卷”或“缠卷”.小明对螺旋线有着浓厚的兴趣,用以下方法画出了如图所示的螺旋线.具体作法是:先作边长为1的正三角形ABC,分别记射线AC,BA,CB为
,
,
,以C为圆心、CB为半径作劣弧
交
于点
;以A为圆心、
为半径作劣弧
交
于点
;以B为圆心、
为半径作劣弧
交
于点
,依此规律,就得到了一系列圆弧形成的螺旋线.记劣弧
的长,劣弧
的长,劣弧
的长,…依次为
,
,
,…,则![](https://staticzujuan.xkw.com/quesimg/Upload/formula/5a004bc7c90ab090e76a37d3a4c58fb3.png)
______ .
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/2e9b0f5f44abbc6544a2f672b025b013.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/3f6f17bc385bafb37e8f964e5eb99cd0.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/c9fce9427c9b17e4d3cda0c3ff3e2e14.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/0d8772aa893a9c1d40f714cb25701701.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/2e9b0f5f44abbc6544a2f672b025b013.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/b1241216f3c1cb5e73043dd1037f556d.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/24bb49fdc6b6bbb2449fdf8a0de769d3.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/2cabc3303519ac16fc998913ad9f349c.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/3f6f17bc385bafb37e8f964e5eb99cd0.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/a18722354086c42e62334983fc50eb6a.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/5b7d857811cbd619f868d951aa7a0ab8.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/11ddc92d84d188c66b435664a7e7b5a4.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/c9fce9427c9b17e4d3cda0c3ff3e2e14.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/97c01fdc7bc471af0b264a04aef0823e.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/0d8772aa893a9c1d40f714cb25701701.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/2cabc3303519ac16fc998913ad9f349c.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/11ddc92d84d188c66b435664a7e7b5a4.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/6c1ccc6c74b8754e9bcbb3f39a11b6f1.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/5a004bc7c90ab090e76a37d3a4c58fb3.png)
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