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有下列命题: ①如果幂函数f (x)=(m2-3m+3)的图象不过原点,则m=l...
有下列命题:
①如果幂函数f (x)=(m
2-3m+3)
![manfen5.com 满分网](http://img.manfen5.com/res/GZSX/web/STSource/20131103100606571734396/SYS201311031006065717343011_ST/0.png)
的图象不过原点,则m=l或2;
②数列{a
n}为等比数列的充要条件为a
n=a
1q
n-1(q为常数):
③已知向量
![manfen5.com 满分网](http://img.manfen5.com/res/GZSX/web/STSource/20131103100606571734396/SYS201311031006065717343011_ST/1.png)
=(t,2),
![manfen5.com 满分网](http://img.manfen5.com/res/GZSX/web/STSource/20131103100606571734396/SYS201311031006065717343011_ST/2.png)
=(-3,6),若向量
![manfen5.com 满分网](http://img.manfen5.com/res/GZSX/web/STSource/20131103100606571734396/SYS201311031006065717343011_ST/3.png)
与
![manfen5.com 满分网](http://img.manfen5.com/res/GZSX/web/STSource/20131103100606571734396/SYS201311031006065717343011_ST/4.png)
的夹角为锐角,则实数t的取值范围是t<4;
④函数f (x)=xsinx在(0,π)上有最大值,没有最小值.
其中正确命题的个数为( )
A.0
B.1
C.2
D.3
考点分析:
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