Asked by Raj

Permutation and combination
A diagonal of a polygon is defined to be a line joining any two non-adjacent vertices.
1.Show that the number of diagonals in a 5 sided polygon is(5 2) -5.

2.how many diagonals are their in 6 sided polygon?

3.Show that the number of diagonals in an n-sided polygon is n(n-2)/2.

Answers

Answered by oobleck
#3 has a typo.
at each vertex, you can draw n-3 diagonals
There are n vertices.
But if you go around, you have drawn each diagonal from both ends, counting it twice.
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