已知△ABC顶点的直角坐标分别为A(3,4),B(0,0),C(c,0 )
(1)若c=5,求sin∠A的值;
(2)若∠A是钝角,求c的取值范围.
考点分析:
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已知
![manfen5.com 满分网](http://img.manfen5.com/res/GZSX/web/STSource/20131103101652031243356/SYS201311031016520312433009_ST/0.png)
与
![manfen5.com 满分网](http://img.manfen5.com/res/GZSX/web/STSource/20131103101652031243356/SYS201311031016520312433009_ST/1.png)
均为单位向量,其夹角为θ,有下列四个命题P
1:|
![manfen5.com 满分网](http://img.manfen5.com/res/GZSX/web/STSource/20131103101652031243356/SYS201311031016520312433009_ST/2.png)
+
![manfen5.com 满分网](http://img.manfen5.com/res/GZSX/web/STSource/20131103101652031243356/SYS201311031016520312433009_ST/3.png)
|>1⇔θ∈[0,
![manfen5.com 满分网](http://img.manfen5.com/res/GZSX/web/STSource/20131103101652031243356/SYS201311031016520312433009_ST/4.png)
);P
2:|
![manfen5.com 满分网](http://img.manfen5.com/res/GZSX/web/STSource/20131103101652031243356/SYS201311031016520312433009_ST/5.png)
+
![manfen5.com 满分网](http://img.manfen5.com/res/GZSX/web/STSource/20131103101652031243356/SYS201311031016520312433009_ST/6.png)
|>1⇔θ∈(
![manfen5.com 满分网](http://img.manfen5.com/res/GZSX/web/STSource/20131103101652031243356/SYS201311031016520312433009_ST/7.png)
,π];P
3:|
![manfen5.com 满分网](http://img.manfen5.com/res/GZSX/web/STSource/20131103101652031243356/SYS201311031016520312433009_ST/8.png)
-
![manfen5.com 满分网](http://img.manfen5.com/res/GZSX/web/STSource/20131103101652031243356/SYS201311031016520312433009_ST/9.png)
|>1⇔θ∈[0,
![manfen5.com 满分网](http://img.manfen5.com/res/GZSX/web/STSource/20131103101652031243356/SYS201311031016520312433009_ST/10.png)
);P
4:|
![manfen5.com 满分网](http://img.manfen5.com/res/GZSX/web/STSource/20131103101652031243356/SYS201311031016520312433009_ST/11.png)
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![manfen5.com 满分网](http://img.manfen5.com/res/GZSX/web/STSource/20131103101652031243356/SYS201311031016520312433009_ST/12.png)
|>1⇔θ∈(
![manfen5.com 满分网](http://img.manfen5.com/res/GZSX/web/STSource/20131103101652031243356/SYS201311031016520312433009_ST/13.png)
,π];其中的真命题是( )
A.P
1,P
4B.P
1,P
3C.P
2,P
3D.P
2,P
4
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