题目
题型:不详难度:来源:
![](http://img.shitiku.com.cn/uploads/allimg/20190921/20190921184022-82690.png)
![](http://img.shitiku.com.cn/uploads/allimg/20190921/20190921184023-63906.png)
![](http://img.shitiku.com.cn/uploads/allimg/20190921/20190921184023-74756.png)
![](http://img.shitiku.com.cn/uploads/allimg/20190921/20190921184024-43434.png)
(1)若
![](http://img.shitiku.com.cn/uploads/allimg/20190921/20190921184024-58728.png)
![](http://img.shitiku.com.cn/uploads/allimg/20190921/20190921184024-98671.png)
(2)设
![](http://img.shitiku.com.cn/uploads/allimg/20190921/20190921184024-64388.png)
![](http://img.shitiku.com.cn/uploads/allimg/20190921/20190921184025-57008.png)
![](http://img.shitiku.com.cn/uploads/allimg/20190921/20190921184025-37825.png)
答案
![](http://img.shitiku.com.cn/uploads/allimg/20190921/20190921184025-74921.png)
![](http://img.shitiku.com.cn/uploads/allimg/20190921/20190921184025-14110.png)
解析
试题分析:(1)利用二倍角公式,化简方程,可得B,利用余弦定理,可求c的值;
(2)利用二倍角、辅助角公式,化简函数,结合A的范围,即可得t取最大值时求A的值 .
试题解析:解:∵
![](http://img.shitiku.com.cn/uploads/allimg/20190921/20190921184026-56292.png)
∴
![](http://img.shitiku.com.cn/uploads/allimg/20190921/20190921184026-27751.png)
∴
![](http://img.shitiku.com.cn/uploads/allimg/20190921/20190921184026-24762.png)
![](http://img.shitiku.com.cn/uploads/allimg/20190921/20190921184025-14110.png)
(1)由
![](http://img.shitiku.com.cn/uploads/allimg/20190921/20190921184026-29123.png)
![](http://img.shitiku.com.cn/uploads/allimg/20190921/20190921184027-98413.png)
即
![](http://img.shitiku.com.cn/uploads/allimg/20190921/20190921184027-38069.png)
![](http://img.shitiku.com.cn/uploads/allimg/20190921/20190921184027-69845.png)
当
![](http://img.shitiku.com.cn/uploads/allimg/20190921/20190921184027-35903.png)
![](http://img.shitiku.com.cn/uploads/allimg/20190921/20190921184024-98671.png)
![](http://img.shitiku.com.cn/uploads/allimg/20190921/20190921184027-35063.png)
![](http://img.shitiku.com.cn/uploads/allimg/20190921/20190921184028-57163.png)
![](http://img.shitiku.com.cn/uploads/allimg/20190921/20190921184025-14110.png)
与三角形内角和定理矛盾,应舍去,∴
![](http://img.shitiku.com.cn/uploads/allimg/20190921/20190921184025-74921.png)
(2)
![](http://img.shitiku.com.cn/uploads/allimg/20190921/20190921184028-23758.png)
![](http://img.shitiku.com.cn/uploads/allimg/20190921/20190921184028-89976.png)
![](http://img.shitiku.com.cn/uploads/allimg/20190921/20190921184028-53172.png)
∵A
![](http://img.shitiku.com.cn/uploads/allimg/20190921/20190921184029-21933.png)
![](http://img.shitiku.com.cn/uploads/allimg/20190921/20190921184029-34850.png)
![](http://img.shitiku.com.cn/uploads/allimg/20190921/20190921184029-77717.png)
![](http://img.shitiku.com.cn/uploads/allimg/20190921/20190921184029-83203.png)
![](http://img.shitiku.com.cn/uploads/allimg/20190921/20190921184030-79499.png)
即
![](http://img.shitiku.com.cn/uploads/allimg/20190921/20190921184030-45409.png)
![](http://img.shitiku.com.cn/uploads/allimg/20190921/20190921184030-57068.png)
当
![](http://img.shitiku.com.cn/uploads/allimg/20190921/20190921184029-77717.png)
![](http://img.shitiku.com.cn/uploads/allimg/20190921/20190921184030-62190.png)
![](http://img.shitiku.com.cn/uploads/allimg/20190921/20190921184025-14110.png)
![](http://img.shitiku.com.cn/uploads/allimg/20190921/20190921184030-99315.png)
核心考点
试题【在中,角的对边分别为,(1)若,求的值; (2)设,当取最大值时求的值。】;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
![](http://img.shitiku.com.cn/uploads/allimg/20190921/20190921183954-64485.png)
![](http://img.shitiku.com.cn/uploads/allimg/20190921/20190921183954-59920.png)
![](http://img.shitiku.com.cn/uploads/allimg/20190921/20190921183954-10381.png)
A.![]() | B.![]() | C.![]() ![]() | D.![]() |
![](http://img.shitiku.com.cn/uploads/allimg/20190921/20190921183910-55036.png)
![](http://img.shitiku.com.cn/uploads/allimg/20190921/20190921183911-79259.png)
![](http://img.shitiku.com.cn/uploads/allimg/20190921/20190921181850-14538.png)
![](http://img.shitiku.com.cn/uploads/allimg/20190921/20190921181850-56984.png)
![](http://img.shitiku.com.cn/uploads/allimg/20190921/20190921181850-52522.png)
![](http://img.shitiku.com.cn/uploads/allimg/20190921/20190921172704-95796.png)
![](http://img.shitiku.com.cn/uploads/allimg/20190921/20190921172705-87225.png)
(1)化简
![](http://img.shitiku.com.cn/uploads/allimg/20190921/20190921172705-24176.png)
(2)设
![](http://img.shitiku.com.cn/uploads/allimg/20190921/20190921172705-64397.png)
![](http://img.shitiku.com.cn/uploads/allimg/20190921/20190921172706-87771.png)
![](http://img.shitiku.com.cn/uploads/allimg/20190921/20190921172704-95796.png)
![](http://img.shitiku.com.cn/uploads/allimg/20190921/20190921172127-73535.png)
![](http://img.shitiku.com.cn/uploads/allimg/20190921/20190921172128-44010.png)
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