引用:
原帖由 235711 於 2007-6-1 05:28 PM 發表
4邊形有2條對角線,4邊形有5條對角線,6邊形有9條對角線,7邊形有14條對角線,看不看到當中的規律?找到規律後很容易就計到了。
Other that observing patterns,
You can calculate it using combinatorics.
Take a point out of the 50 vertex
Each vertex can link to 47 points to join to form a diagonal (since there are 2 adjacent vertices and that point itself, it gives 50-3 = 47)
However, line is calculated 2 times (to join and to be joined)
so it should be 50*47/2 = 1175