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如图,在同心圆中,两圆半径分别为2,1,∠AOB=120°,则阴影部分的面积为(...
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如图,在同心圆中,两圆半径分别为2,1,∠AOB=120°,则阴影部分的面积为( )
A.4π
B.2π
C.
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D.π
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