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(2008•鄂州)如图,Rt△ABC中,∠ACB=90°,∠CAB=30°,BC...
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(2008•鄂州)如图,Rt△ABC中,∠ACB=90°,∠CAB=30°,BC=2,O,H分别为边AB,AC的中点,将△ABC绕点B顺时针旋转120°到△A
1BC
1的位置,则整个旋转过程中线段OH所扫过部分的面积(即阴影部分面积)为( )
A.
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B.
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C.π
D.
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(2008•鄂州)△ABC是半径为
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(2008•鄂州)因为sin30°=
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,所以sin210°=sin(180°+30°)=-sin30°;因为sin45°=
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,所以sin225°=sin(180°+45°)=-sin45°,由此猜想,推理知:一般地当α为锐角时有sin(180°+α)=-sinα,由此可知:sin240°=( )
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B.
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C.
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D.
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