There are 10 possible diagonals drawn from one vertex of the 13-gon which divide it into 11 nonoverlapping triangles.
252 diagonals
There are 119 diagonals.
It has 495 diagonals.
It has 54 diagonals
formula n/2(n-3) so, 13/2(13-3) Diagonal is 65
170
There are 44 diagonals in an 11 sided undecagon
0.5*(152-45) = 90 diagonals
A 20 sided polygon has 170 diagonals
There are 275 diagonals in a 25 sided polygon
39*36/2 = 702 diagonals.