求值:sin230°+cos230°= .
考点分析:
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如图,二次函数y=ax
2+bx+c(a≠0)的图象经过点(-1,2),与y轴交于(0,2)点,且与x轴交点的横坐标分别为x
1、x
2,其中-2<x
1<-1,0<x
2<1,下列结论:①4a-2b+c<0;②2a-b<0;③a<-1;④b
2+8a>4ac.其中正确的有( )
A.1个
B.2个
C.3个
D.4个
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如图,在▱ABCD中,AB:AD=3:2,∠ADB=60°,那么cos∠A的值等于( )
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A.
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B.
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C.
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D.
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下列说法正确的是( )
A.对应边都成比例的多边形相似
B.对应角都相等的多边形相似
C.边数相同的正多边形相似
D.矩形都相似
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已知Rt△ABC中,∠C=90°,BC=9,AB=15,则sinA的值是( )
A.
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B.
![manfen5.com 满分网](http://img.manfen5.com/res/CZSX/web/STSource/20131103000413861581389/SYS201311030004138615813006_ST/1.png)
C.
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D.
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△ABC中,已知∠A=30°,AB=2,AC=4,则△ABC的面积是( )
A.4
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B.4
C.2
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D.2
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