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設原來圓的半徑為r,則直徑為2r,圓的周長為:2πr,圓的面積為:πr2,半徑擴大2倍後,圓的半徑為2r,圓的直徑為4r,圓的周長為:4πr,圓的面積為:(2r)2π=4πr2,周長擴大到原來的:4πr÷2πr=2,面積擴大到…
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