题目
题型:不详难度:来源:
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104034733-37311.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104034733-67716.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104034733-19584.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104034733-37311.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104034733-67716.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104034733-74341.png)
答案
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104034734-47128.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104034734-15976.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104034734-47128.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104034734-47128.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104034734-47128.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104034734-15976.png)
解析
由2、
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104034733-37311.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104034733-67716.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104034733-19584.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104034733-37311.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104034733-67716.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104034733-19584.png)
∴cosA=
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104034734-66077.png)
又∵A∈(0,π),∴A=
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104034734-47128.png)
由
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104034733-19584.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104034733-37311.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104034733-67716.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104034733-74341.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104034733-19584.png)
由正弦定理得
sinC·sinB=
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104034733-19584.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104034734-64881.png)
∴sinC·sin(
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104034735-44138.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104034734-64881.png)
即sinC·(
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104034735-71640.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104034734-66077.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104034734-64881.png)
∴2sinC·cosC+2
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104034733-19584.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104034733-19584.png)
∴sin2C-
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104034733-19584.png)
∴sin(2C-
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104034735-83984.png)
由A=
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104034734-47128.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104034735-44138.png)
∴-
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104034735-83984.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104034735-83984.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104034735-65666.png)
从而2C-
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104034735-83984.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104034735-83984.png)
即C=
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104034734-47128.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104034734-15976.png)
故A=
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104034734-47128.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104034734-15976.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104034734-47128.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104034734-47128.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104034734-47128.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104034734-15976.png)
核心考点
试题【在△ABC中,已知2·=||·||=3||2,求角A,B,C的大小.】;主要考察你对平面向量数量积的意义等知识点的理解。[详细]
举一反三
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104034719-49678.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104034719-87020.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104034719-14761.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104034719-65467.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104034720-71412.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104034720-64809.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104034720-44698.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104034720-72434.png)
①
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104034720-72434.png)
②若
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104034721-68037.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104034720-44698.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104034721-47282.png)
③若
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104034721-86327.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104034720-44698.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104034721-85081.png)
④若
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104034722-41521.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104034722-69499.png)
⑤若
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104034722-55015.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104034719-65467.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104034720-71412.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104034722-24804.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104034714-96904.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104034714-92125.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104034714-80257.png)
A.2 | B.![]() | C.1 | D.![]() |
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104034704-80182.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104034705-29205.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104034705-63774.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104034705-57173.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104034659-21449.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104034659-36958.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104034700-66221.png)
A.1 | B.2 | C.3 | D.5 |
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104034651-33195.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104034651-93051.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104034651-49447.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104034652-21977.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104034652-24034.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104034652-59490.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104034652-36721.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104034653-28116.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104034653-46434.png)
A.![]() | B.![]() | C.![]() | D.![]() |
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