為了瞭解如何分類正多面體的投影，我們先觀察正多面體的一些基本性質和對稱關係。先定義旋轉群和等價類，接著進行初步的正多面體對稱性的分類，再尋找其中的規律性。最後找到一個簡潔的投影分類方式，且適用對象延伸至一些滿足特定規律的多面體。

In order to understand how to classify projections of Platonic solids, we observe the elementary properties and symmetric relations of Platonic solids.
Give a denition of rotation groups and equivalent classes to classify the symmetries of Platonic solids, and ne the regularities of the classication.
Finally, we get a simple way to classify the projections, and the target is
extended to some polyhedrons with some specic symmetric properties.

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