题目内容
已知A、B、P是直线l上三个相异的点,平面内的点O∉l,若正实数x、y满足![](http://thumb.zyjl.cn/pic6/res/gzsx/web/STSource/20131025123035160127091/SYS201310251230351601270014_ST/0.png)
![](http://thumb.zyjl.cn/pic6/res/gzsx/web/STSource/20131025123035160127091/SYS201310251230351601270014_ST/1.png)
【答案】分析:由题意可得,
,而
=(
)(
),展开利用基本不等式即可求解
解答:解:A、B、P是直线l上三个点,且
,
即![](http://thumb.zyjl.cn/pic6/res/gzsx/web/STSource/20131025123035160127091/SYS201310251230351601270014_DA/5.png)
∴![](http://thumb.zyjl.cn/pic6/res/gzsx/web/STSource/20131025123035160127091/SYS201310251230351601270014_DA/6.png)
∴
=(
)(
)
=![](http://thumb.zyjl.cn/pic6/res/gzsx/web/STSource/20131025123035160127091/SYS201310251230351601270014_DA/10.png)
![](http://thumb.zyjl.cn/pic6/res/gzsx/web/STSource/20131025123035160127091/SYS201310251230351601270014_DA/11.png)
=![](http://thumb.zyjl.cn/pic6/res/gzsx/web/STSource/20131025123035160127091/SYS201310251230351601270014_DA/13.png)
当且仅当
即y=![](http://thumb.zyjl.cn/pic6/res/gzsx/web/STSource/20131025123035160127091/SYS201310251230351601270014_DA/15.png)
此时x=4-2
,y=4
-4时取等号
故答案为:![](http://thumb.zyjl.cn/pic6/res/gzsx/web/STSource/20131025123035160127091/SYS201310251230351601270014_DA/18.png)
点评:本题主要考查了向量的共线定理的应用,基本不等式求解最值的应用,解题的关键是
![](http://thumb.zyjl.cn/pic6/res/gzsx/web/STSource/20131025123035160127091/SYS201310251230351601270014_DA/0.png)
![](http://thumb.zyjl.cn/pic6/res/gzsx/web/STSource/20131025123035160127091/SYS201310251230351601270014_DA/1.png)
![](http://thumb.zyjl.cn/pic6/res/gzsx/web/STSource/20131025123035160127091/SYS201310251230351601270014_DA/2.png)
![](http://thumb.zyjl.cn/pic6/res/gzsx/web/STSource/20131025123035160127091/SYS201310251230351601270014_DA/3.png)
解答:解:A、B、P是直线l上三个点,且
![](http://thumb.zyjl.cn/pic6/res/gzsx/web/STSource/20131025123035160127091/SYS201310251230351601270014_DA/4.png)
即
![](http://thumb.zyjl.cn/pic6/res/gzsx/web/STSource/20131025123035160127091/SYS201310251230351601270014_DA/5.png)
∴
![](http://thumb.zyjl.cn/pic6/res/gzsx/web/STSource/20131025123035160127091/SYS201310251230351601270014_DA/6.png)
∴
![](http://thumb.zyjl.cn/pic6/res/gzsx/web/STSource/20131025123035160127091/SYS201310251230351601270014_DA/7.png)
![](http://thumb.zyjl.cn/pic6/res/gzsx/web/STSource/20131025123035160127091/SYS201310251230351601270014_DA/8.png)
![](http://thumb.zyjl.cn/pic6/res/gzsx/web/STSource/20131025123035160127091/SYS201310251230351601270014_DA/9.png)
=
![](http://thumb.zyjl.cn/pic6/res/gzsx/web/STSource/20131025123035160127091/SYS201310251230351601270014_DA/10.png)
![](http://thumb.zyjl.cn/pic6/res/gzsx/web/STSource/20131025123035160127091/SYS201310251230351601270014_DA/11.png)
![](http://thumb.zyjl.cn/pic6/res/gzsx/web/STSource/20131025123035160127091/SYS201310251230351601270014_DA/12.png)
![](http://thumb.zyjl.cn/pic6/res/gzsx/web/STSource/20131025123035160127091/SYS201310251230351601270014_DA/13.png)
当且仅当
![](http://thumb.zyjl.cn/pic6/res/gzsx/web/STSource/20131025123035160127091/SYS201310251230351601270014_DA/14.png)
![](http://thumb.zyjl.cn/pic6/res/gzsx/web/STSource/20131025123035160127091/SYS201310251230351601270014_DA/15.png)
此时x=4-2
![](http://thumb.zyjl.cn/pic6/res/gzsx/web/STSource/20131025123035160127091/SYS201310251230351601270014_DA/16.png)
![](http://thumb.zyjl.cn/pic6/res/gzsx/web/STSource/20131025123035160127091/SYS201310251230351601270014_DA/17.png)
故答案为:
![](http://thumb.zyjl.cn/pic6/res/gzsx/web/STSource/20131025123035160127091/SYS201310251230351601270014_DA/18.png)
点评:本题主要考查了向量的共线定理的应用,基本不等式求解最值的应用,解题的关键是
![](http://thumb.zyjl.cn/pic6/res/gzsx/web/STSource/20131025123035160127091/SYS201310251230351601270014_DA/19.png)
![](http://thumb.zyjl.cn/images/loading.gif)
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