题目内容
已知抛物线
的焦点与椭圆
的右焦点重合,抛物线
的顶点在坐标原点,过点
的直线
与抛物线
交于A,B两点,
(1)写出抛物线
的标准方程 (2)求⊿ABO的面积最小值
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824014258307339.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824014258339823.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824014258307339.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824014258385622.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824014258401280.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824014258307339.png)
(1)写出抛物线
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824014258307339.png)
(1)
(2)16
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824014258463526.png)
试题分析:(1)椭圆
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824014258339823.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824014258495432.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824014258307339.png)
得抛物线的标准方程为
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824014258463526.png)
(2)当直线AB的斜率不存在时,直线方程为
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824014258557368.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824014258588541.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824014258604321.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824014258635697.png)
当直线AB的斜率存在时,设AB的方程为
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824014258666638.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824014258682418.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824014258713979.png)
消去
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824014258729266.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824014258791777.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824014258807771.png)
设A(
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824014258822445.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824014258853480.png)
有
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824014258869648.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824014258900606.png)
∴
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/201408240142589311496.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824014258963878.png)
综上所述,面积最小值为16 13分
点评:抛物线
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824014258978604.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824014258994731.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824014259009766.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824014259025509.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824014259056549.png)
当直线与圆锥曲线相交时,常联立方程借助于方程根与系数的关系求解
![](http://thumb.zyjl.cn/images/loading.gif)
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