题目内容
已知三角形三个顶点的坐标分别为
、
,![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823221113177538.png)
(1)若
,求
的值;
(2)若
,求
的值。
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823221113037553.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823221113162514.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823221113177538.png)
(1)若
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823221113193612.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823221113208242.png)
(2)若
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823221113224341.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823221113240440.png)
(1)![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823221113271539.png)
(2)![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823221113286488.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823221113271539.png)
(2)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823221113286488.png)
本试题主要是考查了向量的数量积的运用,以及结合利用向量的数量积表示夹角的运用。
(1)中利用向量的数量积为零的,得到c的值即可
(2)中根据已知中的点的坐标得到
,然后利用向量的夹角公式得到角A的余弦值,从而得到正弦值。
解:
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/201408232211133335659.png)
(1)中利用向量的数量积为零的,得到c的值即可
(2)中根据已知中的点的坐标得到
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823221113302974.png)
解:
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/201408232211133335659.png)
![](http://thumb2018.1010pic.com/images/loading.gif)
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