题目
题型:不详难度:来源:
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020003112-95538.png)
(1)求函数
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020003112-73700.png)
(2)设△ABC的内角
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020003112-53324.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020003112-87252.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020003112-21171.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020003113-81050.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020003113-95374.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020003113-22489.png)
答案
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020003113-40188.png)
解析
试题分析:(1)利用三角函数的二倍角公式化简f(x),根据三角函数的有界性求出最小值,根据三角函数的周期公式求出f(x)周期.
(2)利用f(C)=0求出角C,利用余弦定理得到边a,b,c的关系;利用向量共线的充要条件得到三角函数的等量关系,利用正弦定理得到边a,b,c的另一个等式,解方程组求出a,b的长.
试题解析:(1)由已知可将函数化简为
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020003114-96292.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020003114-88027.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020003114-71448.png)
(2)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020003114-96246.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020003115-55235.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020003115-10910.png)
而
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020003115-32790.png)
由余弦定理知
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020003115-95166.png)
①②联立可求
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020003113-40188.png)
核心考点
举一反三
A.![]() | B.![]() | C.![]() | D.![]() |
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020003058-36374.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020003058-92423.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020003059-74425.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020003059-49994.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020003059-94746.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020003058-36374.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020003049-31989.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020003049-83994.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020003049-34563.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020003050-46838.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020003050-63508.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020003050-22379.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020003050-77232.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020003050-64036.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020003050-46838.png)
A.10 | B.10![]() | C.20 | D.20![]() |
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020003036-54763.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020003036-70226.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020003036-63783.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020003036-51735.png)
(1)求
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020003037-60754.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020003037-74805.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020003037-43377.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020003036-54763.png)
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