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已知a为锐角,sina=cos50°,则a等于( ) A.20° B.30° C...
已知a为锐角,sina=cos50°,则a等于( )
A.20°
B.30°
C.40°
D.50°
考点分析:
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Rt△ABC中,∠C=90°,如果sinA=
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,那么cosB的值为( )
A.
![manfen5.com 满分网](http://img.manfen5.com/res/CZSX/web/STSource/20131103101443225000287/SYS201311031014432250002008_ST/1.png)
B.
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C.
![manfen5.com 满分网](http://img.manfen5.com/res/CZSX/web/STSource/20131103101443225000287/SYS201311031014432250002008_ST/3.png)
D.不能确定
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已知在Rt△ABC中,∠C=90°.若sinA=
![manfen5.com 满分网](http://img.manfen5.com/res/CZSX/web/STSource/20131103101443225000287/SYS201311031014432250002007_ST/0.png)
,则sinB等于( )
A.
![manfen5.com 满分网](http://img.manfen5.com/res/CZSX/web/STSource/20131103101443225000287/SYS201311031014432250002007_ST/1.png)
B.
![manfen5.com 满分网](http://img.manfen5.com/res/CZSX/web/STSource/20131103101443225000287/SYS201311031014432250002007_ST/2.png)
C.
![manfen5.com 满分网](http://img.manfen5.com/res/CZSX/web/STSource/20131103101443225000287/SYS201311031014432250002007_ST/3.png)
D.1
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在Rt△ABC中,∠C=90°,sinA=
![manfen5.com 满分网](http://img.manfen5.com/res/CZSX/web/STSource/20131103101443225000287/SYS201311031014432250002006_ST/0.png)
,则cosB的值等于( )
A.
![manfen5.com 满分网](http://img.manfen5.com/res/CZSX/web/STSource/20131103101443225000287/SYS201311031014432250002006_ST/1.png)
B.
![manfen5.com 满分网](http://img.manfen5.com/res/CZSX/web/STSource/20131103101443225000287/SYS201311031014432250002006_ST/2.png)
C.
![manfen5.com 满分网](http://img.manfen5.com/res/CZSX/web/STSource/20131103101443225000287/SYS201311031014432250002006_ST/3.png)
D.
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在Rt△ABC中,∠C=90°,下列式子中不一定成立的是( )
A.tanA=
![manfen5.com 满分网](http://img.manfen5.com/res/CZSX/web/STSource/20131103101443225000287/SYS201311031014432250002005_ST/0.png)
B.sin
2A+sin
2B=1
C.sin
2A+cos
2A=1
D.sinA=sinB
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如果α是锐角,且cosα=
![manfen5.com 满分网](http://img.manfen5.com/res/CZSX/web/STSource/20131103101443225000287/SYS201311031014432250002004_ST/0.png)
,那么sinα的值是( )
A.
![manfen5.com 满分网](http://img.manfen5.com/res/CZSX/web/STSource/20131103101443225000287/SYS201311031014432250002004_ST/1.png)
B.
![manfen5.com 满分网](http://img.manfen5.com/res/CZSX/web/STSource/20131103101443225000287/SYS201311031014432250002004_ST/2.png)
C.
![manfen5.com 满分网](http://img.manfen5.com/res/CZSX/web/STSource/20131103101443225000287/SYS201311031014432250002004_ST/3.png)
D.2
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