已知数列
是公差不为0的等差数列,且
,则数列
的前2021项和为( )
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/034ba25825c13725931c483aa47c9363.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/14ab4a389aa3d8fed4919525958c9e50.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/034ba25825c13725931c483aa47c9363.png)
A.![]() | B.![]() | C.2021 | D.4042 |
更新时间:2021-08-17 16:11:36
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【推荐1】设等差数列
的前n项和为
,
,公差为d,
,
.则下列结论不 正确的是( )
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/83cf38189d5cbf627d2b82ac0eb76006.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/08eb71ecf8d733b6932f4680874dbbf3.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/179513ce80436471efbe1d9b31735f7d.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/22eaff238f56c11aa4cf5bf990d0de31.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/ad2c7ea71dea644181a904484bb36da8.png)
A.![]() | B.当![]() ![]() |
C.![]() | D.使得![]() |
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【推荐1】设等差数列
的前n项和为
,若
;则
等于( )
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/83cf38189d5cbf627d2b82ac0eb76006.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/08eb71ecf8d733b6932f4680874dbbf3.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/5235e0757b0d033de500a3aae4b5e807.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/05201ef79a5d5904f492845396fb5470.png)
A.18 | B.36 | C.45 | D.60 |
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【推荐2】已知
为等比数列,数列
满足
,且
,则数列
的前
项和为( )
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/b4be2164a2c67d6163faee87a10942bb.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/43b7e7cd571c8cd141cbbfe5d0890bf6.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/e3925fea2d79c2bb4cb8a142f4a09f66.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/804947da9fcd30025081ff14dc6b3300.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/43b7e7cd571c8cd141cbbfe5d0890bf6.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/b6a24198bd04c29321ae5dc5a28fe421.png)
A.![]() | B.![]() | C.![]() | D.![]() |
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【推荐3】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
,分别记射线
,
,
为
,
,
,以
为圆心、
为半径作劣弧
交
于点
;以
为圆心、
为半径作劣弧
交
于点
;以
为圆心、
为半径作劣弧
交
于点
,…,依此规律作下去,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://img.xkw.com/dksih/QBM/2021/4/10/2696703180005376/2696742320873472/STEM/1126a47a85b944a3a66dcc413087f1f3.png?resizew=233)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/7bef5239ddbb0972700ce01daf9ee7cf.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/60ef95894ceebaf236170e8832dcf7e3.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/7dea2ae9d515f9ab351ad72306b776ee.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/6b1bd1adfe4cc6566218f19970c2fd3b.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/2e9b0f5f44abbc6544a2f672b025b013.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/3f6f17bc385bafb37e8f964e5eb99cd0.png)
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A.![]() | B.![]() | C.![]() | D.![]() |
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