题目
题型:不详难度:来源:
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020035236-71749.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020035237-14636.png)
答案
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020035237-36725.png)
解析
试题分析:(1)∵A+B+C=180°,∴cosC=cos(180°-A-B)=-cos(A+B)=-
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020035237-81616.png)
∴cosC=-
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020035237-81616.png)
(2)∵a、b是方程
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020035236-71749.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020035237-27142.png)
∴
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020035237-24189.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020035238-21238.png)
点评:中档题,本题综合性较强,综合考查三角函数诱导公式,韦达定理的应用,余弦定理的应用。解答中注意应用了a+b,ab的整体代换,简化了解答过程。
核心考点
举一反三
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020035233-19008.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020035233-35707.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020035233-13664.png)
A.
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020035233-36378.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020035233-68207.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020035233-63707.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020035234-65280.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020035225-31201.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020035225-97837.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020035225-18918.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020035225-61098.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020035225-27610.png)
(Ⅰ)求角B的值;
(Ⅱ)如果
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020035225-24963.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020035225-31201.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020035219-42139.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020035219-51533.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020035219-97389.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020035220-11450.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020035214-37074.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020035214-11730.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020035208-46748.png)
A.![]() | B.![]() | C.![]() | D.![]() |
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