题目
题型:不详难度:来源:
在
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020053904-64543.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020053904-39235.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020053904-21922.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020053904-70683.gif)
(Ⅰ)求角
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020053904-14521.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020053904-92677.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020053904-64543.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020053905-23254.gif)
答案
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020053904-70683.gif)
由正弦定理及余弦定理得
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020053905-77554.gif)
∴
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020053905-63784.gif)
由余弦定理得
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020053905-87002.gif)
∵
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020053905-82139.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020053905-86613.gif)
另解:∵
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020053904-70683.gif)
∴
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020053906-10845.gif)
∵
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020053905-82139.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020053906-78568.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020053906-88701.gif)
∵
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020053905-82139.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020053905-86613.gif)
(Ⅱ) 由已知及(Ⅰ)知得
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020053906-90619.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020053906-47204.gif)
∴
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020053907-41983.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020053907-50636.gif)
∴当
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020053907-50636.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020053904-64543.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020053907-66539.gif)
解析
核心考点
举一反三
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020053858-80263.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020053858-94371.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020053859-84704.png)
A.![]() | B.![]() | C.![]() | D.![]() |
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020053851-85633.gif)
(Ⅰ)A的大小;
(Ⅱ)若
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020053851-81840.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020053852-28057.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020053846-49345.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020053846-37453.gif)
(I)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020053847-71524.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020053846-49345.gif)
(II)求
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020053847-84793.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020053839-89773.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020053839-68636.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020053839-53282.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020053840-60017.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020053839-89773.png)
A.![]() | B.![]() | C.![]() | D.![]() |
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020053835-29532.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020053835-60712.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020053836-82969.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020053836-13977.png)
则
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020053835-29532.png)
A.直角三角形 | B.钝角三角形 | C.等腰直角三角形 | D.等边三角形 |
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