名校
解题方法
1 . 已知首项为1的数列
的前
项和为
,其中
,现有以下结论:①
;②
;③
.则正确结论的序号为( )
![](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/5de33eee3f30cd929620f7f52069c894.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/f801629bc14181f7e0cd2aa67c22b527.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/cb0eda61a7d9fc046aac897b6073c52b.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/4abf15ab668060c0fc89a73dbfd57d5f.png)
A.① | B.② | C.②③ | D.①②③ |
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2 . 以下各说法中:
①已知在边长为
的等边三角形
中, 则
;
②若两非零向量
,若
,则
的夹角为锐角;
③已知大小分别为
与
的两个力,要使合力大小恰为
,则它们的夹角的余弦值为
;
④已知数列
的通项
,其前
项和为
,则使
最小的
值为
.
其中正确说法的有________ .(填写所有正确的序号)
①已知在边长为
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/b8860d9787671b53b1ab68b3d526f5ca.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/0faed94a64b2dcfc6801b4fca0f16675.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/05e919aa6826aa94858c261bf05d0e18.png)
②若两非零向量
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/a8ccba3b87a8a48ac3dd5f72d00bdb1a.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/90eb96b770a4bed15037b68a77eb9667.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/a8ccba3b87a8a48ac3dd5f72d00bdb1a.png)
③已知大小分别为
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/bf98e72511232b14b841a5d35a607653.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/d8e74032b421b3c8e6323bcf6af9aee6.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/3842600c36ce94156ce8ecb6463a288f.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/56d266a04f3dc7483eddbc26c5e487db.png)
④已知数列
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/63d471926f7b27322d90c82b9ce21d3d.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/67c4593f37ce523cfa8fb5c102240319.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/08eb71ecf8d733b6932f4680874dbbf3.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/b6a24198bd04c29321ae5dc5a28fe421.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/d91e07104b699c4012be2d26160976a2.png)
其中正确说法的有
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