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1旋转的秘密如图所示,两枚同面值的硬币紧贴在一起。硬币B固定不动,硬币A的边缘紧贴B并围绕着B旋转。当A围绕着B旋转一周回到原来的位置
1 The secret of the rotation As shown in the figure, two coins of the same value are closely attached. Coin B is immovable, the edge of coin A is close to B and rotates around B. When A rotates around B to return to its original position