在邊長為
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824032217144206.png)
的正方形
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824032217159534.png)
中,
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824032217175399.png)
為
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824032217175395.png)
的中點,點
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824032217190318.png)
在線段
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824032217206396.png)
上運動,則
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824032217222614.png)
的最大值為___________.
試題分析:由于點
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824032217190318.png)
在運動,故向量
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824032217268500.png)
,
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824032217300427.png)
都在變化,但我們可以把它們用同一個變化量與不變量表示出來,
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824032217300717.png)
,
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824032217300427.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824032217346601.png)
,注意到
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824032217362415.png)
與
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824032217378624.png)
都垂直,因此
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824032217222614.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824032217409164.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824032217440926.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824032217440833.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824032217502639.png)
,而
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824032217502465.png)
最大值為
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824032217518496.png)
,故所求最大值為
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824032217237389.png)
.
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