此刻你只能有两种操作：线或弧。
用于表示圆或弧的中心，还可表示对称。
Use to indicate the centers of circles and arcs, and to represent symmetry.
用尺规将一个任意角或弧绝对准确三等分是不可能的。
It is impossible to divide a given common Angle or arc (instead of the particular angles or arcs) into three equal parts by using a rule and compasses.
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