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圓的面積S=πR²;(R是圓的半徑) 圓的弧長L=|α|*R(|α|是弧度制的圓心角,R是圓的半徑) 扇形面積S=1/2*L*R(L是扇形的弧長R是圓的半徑) 或者=1/2*|α|*R²;(|α|是弧度制的圓心角,R是圓的半徑)
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