(2006•达州)先阅读短文,再解答短文后面的问题.
规定了方向的线段称为有向线段.比如,对于线段AB,规定以A为起点,B为终点,便可得到一条从A到B的有向线段.为强调其方向,我们在其终点B处画上箭头(如下图-1).以A为起点,B为终点的有向线段记为
![manfen5.com 满分网](http://img.manfen5.com/res/CZSX/web/STSource/20131021231858083262347/SYS201310212318580832623003_ST/0.png)
(起点字母A写在前面,终点字母B写在后面).线段AB的长度叫做有向线AB的长度(或模),记为|
![manfen5.com 满分网](http://img.manfen5.com/res/CZSX/web/STSource/20131021231858083262347/SYS201310212318580832623003_ST/1.png)
|.显然,有向线段
![manfen5.com 满分网](http://img.manfen5.com/res/CZSX/web/STSource/20131021231858083262347/SYS201310212318580832623003_ST/2.png)
和有向线段
![manfen5.com 满分网](http://img.manfen5.com/res/CZSX/web/STSource/20131021231858083262347/SYS201310212318580832623003_ST/3.png)
长度相同.方向不同,它们不是同一条有向线段.
对于同一平面内的有向线段,我们可以在该平面建立直角坐标系进行研究(一般情况,直角坐标系的单位长度与有向线段的单位长度相同).比如,以坐标原点O(0,0)为起点,P(3,0)为终点的有向线段
![manfen5.com 满分网](http://img.manfen5.com/res/CZSX/web/STSource/20131021231858083262347/SYS201310212318580832623003_ST/4.png)
,其方向与x轴正方向相同,长度(或模)是|
![manfen5.com 满分网](http://img.manfen5.com/res/CZSX/web/STSource/20131021231858083262347/SYS201310212318580832623003_ST/5.png)
|=3.
问题:
(1)在如图所示的平面直角坐标系中画出
![manfen5.com 满分网](http://img.manfen5.com/res/CZSX/web/STSource/20131021231858083262347/SYS201310212318580832623003_ST/6.png)
有向线段,使得
![manfen5.com 满分网](http://img.manfen5.com/res/CZSX/web/STSource/20131021231858083262347/SYS201310212318580832623003_ST/7.png)
=3
![manfen5.com 满分网](http://img.manfen5.com/res/CZSX/web/STSource/20131021231858083262347/SYS201310212318580832623003_ST/8.png)
,
![manfen5.com 满分网](http://img.manfen5.com/res/CZSX/web/STSource/20131021231858083262347/SYS201310212318580832623003_ST/9.png)
与x轴正半轴的夹角是45°,且与y轴的负半轴的夹角是45°;
(2)若有向线段
![manfen5.com 满分网](http://img.manfen5.com/res/CZSX/web/STSource/20131021231858083262347/SYS201310212318580832623003_ST/10.png)
的终点B的坐标为(3,
![manfen5.com 满分网](http://img.manfen5.com/res/CZSX/web/STSource/20131021231858083262347/SYS201310212318580832623003_ST/11.png)
),试求出它的模及它与x轴正半轴的夹角;
(3)若点M、A、P在同一直线上,
![manfen5.com 满分网](http://img.manfen5.com/res/CZSX/web/STSource/20131021231858083262347/SYS201310212318580832623003_ST/12.png)
成立吗?试画出示意图加以说明.(示意图可以不画在平面直角坐标系中)
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