题目
题型:不详难度:来源:
![](http://img.shitiku.com.cn/uploads/allimg/20191105/20191105031807-83938.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191105/20191105031807-33732.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191105/20191105031807-42543.gif)
(1)若⊿ABC为正三角形,求证:
![](http://img.shitiku.com.cn/uploads/allimg/20191105/20191105031808-38823.gif)
(2)若
![](http://img.shitiku.com.cn/uploads/allimg/20191105/20191105031808-38823.gif)
答案
解析
![](http://img.shitiku.com.cn/uploads/allimg/20191105/20191105031808-18809.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191105/20191105031808-83505.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191105/20191105031808-31207.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191105/20191105031808-31207.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191105/20191105031808-94749.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191105/20191105031808-94749.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191105/20191105031808-83505.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191105/20191105031809-36743.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191105/20191105031808-38823.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191105/20191105031809-56934.gif)
(2)若
![](http://img.shitiku.com.cn/uploads/allimg/20191105/20191105031808-38823.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191105/20191105031809-58048.gif)
∴
![](http://img.shitiku.com.cn/uploads/allimg/20191105/20191105031810-23309.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191105/20191105031810-75064.gif)
两式两边分别相乘得
![](http://img.shitiku.com.cn/uploads/allimg/20191105/20191105031810-54577.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191105/20191105031810-47682.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191105/20191105031811-63857.gif)
解法二:依题意有
![](http://img.shitiku.com.cn/uploads/allimg/20191105/20191105031811-68495.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191105/20191105031811-81234.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191105/20191105031811-26253.gif)
同理
![](http://img.shitiku.com.cn/uploads/allimg/20191105/20191105031812-96552.gif)
核心考点
举一反三
![](http://img.shitiku.com.cn/uploads/allimg/20191105/20191105031800-90427.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191105/20191105031800-88658.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191105/20191105031800-11527.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191105/20191105031801-44053.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191105/20191105031800-11527.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191105/20191105031800-88658.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191105/20191105031801-56740.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191105/20191105031801-25838.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191105/20191105031801-25838.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191105/20191105031801-25838.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191105/20191105031800-11527.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191105/20191105031801-64631.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191105/20191105031800-90427.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191105/20191105031801-56740.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191105/20191105031800-90427.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191105/20191105031801-56740.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191105/20191105031800-11527.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191105/20191105031801-25838.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191105/20191105031800-88658.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191105/20191105031720-23535.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191105/20191105031720-64464.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191105/20191105031720-67022.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191105/20191105031720-51476.jpg)
![](http://img.shitiku.com.cn/uploads/allimg/20191105/20191105031714-51039.jpg)
平面上的向量
![](http://img.shitiku.com.cn/uploads/allimg/20191105/20191105031715-44676.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191105/20191105031715-36766.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191105/20191105031715-61792.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191105/20191105031715-94686.gif)
则
![](http://img.shitiku.com.cn/uploads/allimg/20191105/20191105031716-64044.gif)
A.![]() | B.![]() | C.![]() | D.以上均不对 |
![](http://img.shitiku.com.cn/uploads/allimg/20191105/20191105031702-34263.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191105/20191105031703-56332.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191105/20191105031703-88055.png)
A.![]() | B.![]() | C.![]() | D.![]() |
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