中三數學 reflection & rotation

2015-05-24 8:10 pm

number of planes of reflection and rotation symmetry 有冇一個定律去計?

一般正方體和正三角體尚可以死背數字應付, 但遇上題目係更多邊形, 如19-gonal prism, 21-gonal pyramid, 該如何處理?

回答 (1)

邊位都好

2015-05-24 9:10 pm

✔ 最佳答案

除咗正多面體 (包括你講嘅正方體及正三角錐體，即正四面體)，底部係正多邊形嘅柱體同錐體，都係有公式的：number of planes of reflection for n-gonal prism is (n + 1),number of axis of rotation symmetry for n-gonal prism is also (n + 1).number of planes of reflection for n-gonal pyramid is n,number of axis of rotation symmetry for n-gonal pyramid is 1.
所以，19-gonal prism 有 20 塊 planes of reflection, 20 條 rotation symmetry.21-gonal pyramid 有 21 塊 planes of reflection, 1 條 rotation symmetry.

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