名校
1 . 下列命题错误的个数是( )
①在
中,
是
的充要条件;
②若向量
满足
,则
与
的夹角为钝角;
③若数列
的前
项和
,则数列
为等差数列;
④若
,则“
”是“
”的必要不充分条件.
①在
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/0faed94a64b2dcfc6801b4fca0f16675.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/19dc38d888741a1b2e95fe0773a48c38.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/ca51be437b1a97ca92aa1159ab71102c.png)
②若向量
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/a8ccba3b87a8a48ac3dd5f72d00bdb1a.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/5f8139fb7861111f2a99f559d72f829e.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/cb80eb942aafb194fadc473776f35b1d.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/433b94c39737727e53468df419d8314a.png)
③若数列
![](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/f9b8c236da8cf6588d3f31e2461543b4.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/83cf38189d5cbf627d2b82ac0eb76006.png)
④若
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/e1e69392d21261afd8e5e5f096634669.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/d2e39ed1fa73c58f8614ab27edb32699.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/1d33da711e50e96568facb18cef27165.png)
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A.1 | B.2 | C.3 | D.4 |