在銳角△
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824010328055234.png)
中,
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824010328070203.png)
、
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824010328086207.png)
、
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824010328102200.png)
分別為角
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824010328117206.png)
、
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824010328133206.png)
、
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824010328164204.png)
所對的邊,且
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824010328164314.png)
(1)確定角
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824010328164204.png)
的大��;
(2)若
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824010328195250.png)
,且△
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824010328055234.png)
的面積為
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824010328242280.png)
,求
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824010328398233.png)
的值.
(1)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824010328414235.png)
(2)5
試題分析:(1)由
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824010328164314.png)
得
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824010328445241.png)
sinA="2sinC" sinA
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824010328460188.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824010328445241.png)
="2" sinC
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824010328460188.png)
C=
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824010328414235.png)
(2)由(1)知sinC=
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824010328523265.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824010328460188.png)
又△
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824010328055234.png)
的面積為
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824010328242280.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/201408240103285859140.jpg)
點評:熟練掌握正余弦定理及其變形是解決此類問題的關(guān)鍵,屬基礎(chǔ)題
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