题目
题型:不详难度:来源:
![](http://img.shitiku.com.cn/uploads/allimg/20190921/20190921094937-22260.png)
![](http://img.shitiku.com.cn/uploads/allimg/20190921/20190921094937-32506.png)
(1)求函数f(x)的最小值和最小正周期;
(2)设△ABC的内角A、B、C的对边分别为a、b、c,且c=
![](http://img.shitiku.com.cn/uploads/allimg/20190921/20190921094937-62096.png)
答案
解析
![](http://img.shitiku.com.cn/uploads/allimg/20190921/20190921094937-22260.png)
![](http://img.shitiku.com.cn/uploads/allimg/20190921/20190921094937-85018.png)
![](http://img.shitiku.com.cn/uploads/allimg/20190921/20190921094937-32506.png)
![](http://img.shitiku.com.cn/uploads/allimg/20190921/20190921094938-59508.png)
![](http://img.shitiku.com.cn/uploads/allimg/20190921/20190921094938-29781.png)
(2)f(C)=sin(2C-
![](http://img.shitiku.com.cn/uploads/allimg/20190921/20190921094938-59508.png)
![](http://img.shitiku.com.cn/uploads/allimg/20190921/20190921094938-59508.png)
∵0<C<π,
∴-
![](http://img.shitiku.com.cn/uploads/allimg/20190921/20190921094938-59508.png)
![](http://img.shitiku.com.cn/uploads/allimg/20190921/20190921094938-59508.png)
![](http://img.shitiku.com.cn/uploads/allimg/20190921/20190921094938-44913.png)
![](http://img.shitiku.com.cn/uploads/allimg/20190921/20190921094938-59508.png)
![](http://img.shitiku.com.cn/uploads/allimg/20190921/20190921094938-39799.png)
![](http://img.shitiku.com.cn/uploads/allimg/20190921/20190921094939-65689.png)
∵sin B=2sin A及正弦定理,得b=2a.①
由余弦定理,得c2=a2+b2-2abcos
![](http://img.shitiku.com.cn/uploads/allimg/20190921/20190921094939-65689.png)
![](http://img.shitiku.com.cn/uploads/allimg/20190921/20190921094937-62096.png)
∴a2+b2-ab=3,②
由①②联立,得a=1且b=2.
核心考点
试题【已知函数f(x)=sin 2x-cos2x-,x∈R.(1)求函数f(x)的最小值和最小正周期;(2)设△ABC的内角A、B、C的对边分别为a、b、c,且c=,】;主要考察你对两角和与差的三角函数等知识点的理解。[详细]
举一反三
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A.![]() | B.![]() | C.![]() ![]() | D.![]() |
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