题目
题型:不详难度:来源:
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020045923-16551.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020045923-26069.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020045923-90962.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020045923-81377.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020045924-96397.png)
(1)求
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020045923-16551.png)
(2)若
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020045924-80631.png)
答案
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020045924-96690.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020045924-23698.png)
解析
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020045924-75328.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020045923-81377.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020045924-98267.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020045923-16551.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020045924-96690.png)
第二问中,∵a =7 ∴c=5由余弦定理得:
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020045924-95660.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020045925-79430.png)
又C为内角 ∴
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020045924-23698.png)
解:(1)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020045925-17959.png)
又∵
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020045923-81377.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020045924-98267.png)
∴
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020045923-16551.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020045924-96690.png)
(2)∵a =7 ∴c=5 ……………………7分
由余弦定理得:
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020045925-98336.png)
∴
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020045925-44528.png)
又由余弦定理得:
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020045925-79430.png)
又C为内角 ∴
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020045924-23698.png)
另解:由正弦定理得:
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020045925-51177.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020045925-34215.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020045926-62826.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020045924-23698.png)
核心考点
举一反三
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020045918-42271.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020045918-73406.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020045919-53368.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020045918-42271.png)
A.![]() | B.![]() | C.3 | D.6 |
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020045914-69779.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020045914-81029.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020045914-12011.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020045914-20959.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020045915-45997.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020045914-20959.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020045908-79050.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020045908-23473.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020045908-43810.png)
(1)求
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020045908-40408.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020045908-40708.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020045908-20974.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020045901-90217.png)
(1)求
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020045901-16969.png)
(2)若
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020045902-19396.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020045858-84020.png)
A.120° | B.60° | C.150° | D.30° |
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