How many diagonals are in a triskaidecagon?

Answer 1

65.

The number of diagonals in a polygon with n sides is given by:

diagonals = n(n - 3) / 2

So for a triskaidecagon which has 13 sides n = 13 and:

number_of_diagonals = 13(13 - 3) /2

= 13 x 10 / 2

= 65