裁缝用的划粉其形状是令人着迷的.要作成划粉形,可以从等边三角形开始.以每一顶点为圆心,以三角形边长为半径,作弧经过另外两顶点即可.划粉形可以内接于一个正方形,当它被放在外接正方形中时,它能紧贴着正方形旋转(想一想,为什么?).作为这 The shape of the powder used by tailors is fascinating. To make a powder, you can start from an equilateral triangle. Take each vertex as the center of the circle, and use the length of the triangle as the radius. Make the arc pass through the other two vertices. The powder can be inscribed in a square. When it is placed in an external square, it can rotate against the square (think, why?). As this