题目
题型:不详难度:来源:
如图,在△ABC中,
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020042219-46959.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020042219-15191.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020042220-47607.png)
(1)求
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020042220-14284.png)
(2)设
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020042220-51631.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020042220-27630.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020042220-80149.png)
答案
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020042220-25826.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020042221-37728.png)
(2)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020042221-13845.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020042221-46780.png)
解析
试题分析:(1)由
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020042219-15191.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020042221-70063.png)
得
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020042221-49683.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020042222-78729.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020042221-37728.png)
(2)在△ABC中,由正弦定理,
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020042222-61833.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020042222-34519.png)
又在△ADC中,
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020042222-41216.png)
由余弦定理得,
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020042222-18542.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020042221-46780.png)
点评:典型题,在利用三角函数恒等变换解题过程中,“变角、变号、变名”是常用技巧,为研究三角函数的性质,往往要先将函数“化一”。(2)小题综合应用正弦定理、余弦定理,体现运用数学知识的灵活性。
核心考点
举一反三
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020042210-18348.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020042210-64824.png)
(Ⅰ)求角C的大小:
(Ⅱ)设角
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020042210-68938.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020042210-17300.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020042210-50111.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020042211-72911.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020042211-33889.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020042205-91781.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020042205-51559.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020042205-67759.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020042205-28131.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020042206-28915.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020042206-30635.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020042206-14644.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020042206-16248.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020042206-53781.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020042207-81104.png)
A.8 | B.16 | C.32. | D.64 |
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020042155-11928.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020042156-98227.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020042156-82944.png)
(Ⅰ)当
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020042156-60093.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020042156-93772.png)
(Ⅱ)在
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020042156-82127.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020042157-13689.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020042157-67757.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020042157-21911.png)
若a、b、c是△ABC三个内角A、B、C所对边,且
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020042148-88690.png)
(1)求
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020042148-87167.png)
(2)当
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020042149-44857.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020042149-56168.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020042146-12450.png)
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