1 . 对于数列
,存在
,使得不等式
成立,则下列说法正确的有______ .(请写出所有正确说法的序号).
①数列
为等差数列;
②数列
为等比数列;
③若
,则
;
④若
,则数列
的前
项和
.
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/83cf38189d5cbf627d2b82ac0eb76006.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/c4166972dec0aa3e8694a44eeb941a08.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/d3508ddcc21ef2161f8cc6052e472025.png)
①数列
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/83cf38189d5cbf627d2b82ac0eb76006.png)
②数列
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/83cf38189d5cbf627d2b82ac0eb76006.png)
③若
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/039e4fe671d61e59b96ee525c9df43e8.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/40535f714f70909054e227e820182055.png)
④若
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/039e4fe671d61e59b96ee525c9df43e8.png)
![](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/cac691e1188206c647119a564d8b4f2b.png)
您最近一年使用:0次
解题方法
2 . 对于
ABC,有如下命题:
①若sin2A=sin2B,则
ABC为等腰三角形;
②若sinA=cosB,则
ABC为直角三角形;
③若sin2A+sin2B+cos2C<1,则
ABC为钝角三角形;
④若满足C=
,c=4,a=x的三角形有两个,则实数x的取值范围为(4,8).
其中正确说法的序号是_____ .
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/ce4cba95fc7d4853a243f8e3fb20ce70.png)
①若sin2A=sin2B,则
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/ce4cba95fc7d4853a243f8e3fb20ce70.png)
②若sinA=cosB,则
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/ce4cba95fc7d4853a243f8e3fb20ce70.png)
③若sin2A+sin2B+cos2C<1,则
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/ce4cba95fc7d4853a243f8e3fb20ce70.png)
④若满足C=
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/c67d01e61dc0042e67b5e8ec8e727c22.png)
其中正确说法的序号是
您最近一年使用:0次