题目内容
(本小题满分12分)设向量
,
,其中
.
(1)若
,求
的值;
(2)求△
面积的最大值.
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823184402295575.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823184402311527.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823184402327481.gif)
(1)若
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823184402342413.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823184402358270.gif)
(2)求△
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823184402373274.gif)
(1)解:依题意得,
,……………………… 2分
所以![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823184402436993.gif)
,……………………………………………4分
所以
.
因为
,所以
.…………………………………………………………6分
(2)解:由
,得
.…………………………………8分
所以![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823184402561945.gif)
,………………………………10分
所以当
时,△
的面积取得最大值
.…………12分
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823184402405976.gif)
所以
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823184402436993.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823184402451745.gif)
所以
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823184402467471.gif)
因为
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823184402498321.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823184402514348.gif)
(2)解:由
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823184402327481.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823184402545579.gif)
所以
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823184402561945.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/201408231844025761259.gif)
所以当
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823184402592291.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823184402373274.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823184402623227.gif)
略
![](http://thumb2018.1010pic.com/images/loading.gif)
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