题目内容
求满足下列条件的直线方程:
(1)经过两条直线
和
的交点,且平行于直线
;
(2)经过两条直线
和
的交点,且垂直于直线
.
(1)经过两条直线
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824013319968669.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824013319983669.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824013320092519.png)
(2)经过两条直线
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824013320108628.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824013320170579.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824013320202597.png)
(1)
(2)![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824013320248622.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824013320233553.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824013320248622.png)
试题分析:(1)联立两直线方程
得
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/201408240133202801096.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824013320295250.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824013320326691.png)
即两直线交点坐标为
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824013320342493.png)
∵所求直线与已知直线平行.
∴设直线方程
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824013320373680.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824013320404394.png)
∴直线
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824013320420651.png)
(2)联立两直线方程
得
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824013320451992.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824013320295250.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824013320482709.png)
即两直线交点坐标为
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824013320514508.png)
∵所求直线与已知直线垂直.
∴设直线方程
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824013320529783.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824013320560423.png)
∴直线
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824013320576737.png)
点评:两直线的交点即方程组的解,两直线平行,斜率相等,两直线垂直,斜率相乘等于
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824013320592222.png)
![](http://thumb.zyjl.cn/images/loading.gif)
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