题目
题型:不详难度:来源:
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104035850-90926.png)
答案
解析
所以(a+b)·c=-x-3y=5,|c|=
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104035850-94483.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104035850-90926.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104035851-18681.png)
解得
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104035851-67648.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104035851-31520.png)
不妨取
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104035851-15506.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104035851-96941.png)
设a与c的夹角为θ,
则cosθ=
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104035852-19382.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104035852-95056.png)
=-
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104035852-43833.png)
因为0°≤θ≤180°,所以θ=120°.
核心考点
试题【已知向量a=(1,3),b=(-2,-6),|c|=,若(a+b)·c=5,则a与c的夹角为__________.】;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/20191104/20191104035840-41698.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104035840-86931.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104035840-36959.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104035834-51283.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104035835-41575.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104035835-52943.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104035835-90750.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104035836-96116.png)
A.5 | B.6 | C.7 | D.8 |
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104035823-36990.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104035823-97508.png)
(1)求椭圆C的方程;
(2)点A为椭圆C的右顶点,过点
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104035823-72625.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104035823-34953.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104035823-88631.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104035824-34663.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104035807-80272.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104035807-65393.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104035808-23340.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104035808-63311.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104035808-77658.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104035809-87709.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104035809-16818.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104035809-74603.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104035759-65395.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104035800-41967.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104035800-42648.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104035759-65395.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104035800-65480.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104035759-65395.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104035800-98928.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104035801-89375.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191104/20191104035801-70833.png)
A.![]() | B.![]() | C.![]() | D.![]() |
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