题目内容
(本小题满分12分)已知
,其中![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823163420144840.gif)
,若
图象中相邻的对称轴间的距离不小于
..
(1)求
的取值范围;
(2)在
中,
分别为角
的对边.且
,当
最大时.求
面积.
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823163420128486.gif)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823163420144840.gif)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823163420159883.gif)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823163420175270.gif)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823163420206233.gif)
(1)求
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823163420222201.gif)
(2)在
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823163420222400.gif)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823163420284260.gif)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823163420300291.gif)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823163420315648.gif)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823163420222201.gif)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823163420222400.gif)
(1)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823163420502304.gif)
(2)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823163420518270.gif)
解:(1)![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/201408231634206901363.gif)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823163420705671.gif)
……………………3分
由题意知![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823163420752589.gif)
……………………6分
(2)由于
1,由于(1)知
的最大值为1,
又![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823163420908665.gif)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823163420939577.gif)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823163420955408.gif)
由余弦定理得
,又![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823163421002272.gif)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823163421017421.gif)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823163421048277.gif)
……………………12分
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/201408231634206901363.gif)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823163420705671.gif)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823163420736633.gif)
由题意知
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823163420752589.gif)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823163420783320.gif)
(2)由于
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823163420799759.gif)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823163420222201.gif)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823163420892646.gif)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823163420908665.gif)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823163420939577.gif)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823163420955408.gif)
由余弦定理得
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823163420986351.gif)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823163421002272.gif)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823163421017421.gif)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823163421048277.gif)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823163421111739.gif)
![](http://thumb.zyjl.cn/images/loading.gif)
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