名校
1 . 给出下列五个命题:
①直线
平行于平面
内的一条直线,则
;
②若
是锐角三角形,则
;
③已知
是等差数列
的前
项和,若
,则
;
④当
时,不等式
恒成立,则实数
的取值范围为
.
其中正确命题的序号为___________ .
①直线
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/0f85fca60a11e1af2bf50138d0e3fe62.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/e170f206fdbbd834aad7580c727e2cc6.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/87446a7f3d8663e3fa62157adcbe2835.png)
②若
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/15c0dbe3c080c4c4636c64803e5c1f76.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/30c77720b8b287e64c5e840dcc8db528.png)
③已知
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/08eb71ecf8d733b6932f4680874dbbf3.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/effdf8cadd1a54cb5e0f3a621dd4ea80.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/a68405af59395b5b557581b32f97a5ca.png)
④当
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/1864b98153200f5929787295de2c1e38.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/1e9bd06dbb60db9ef56db0d694505330.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/294f5ba74cdf695fc9a8a8e52f421328.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/a7b06647930e162809da06a1a72b9d9f.png)
其中正确命题的序号为
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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