Question 1023060
*[illustration polygons.jpg]

See how a rectangle (4 sides) can be cut into 2 triangles?
And a pentagon (5 sides) cut into 3 

Any N-gon, can be cut into N-2 triangles and the total degrees is 180 (N-2). Think about this, draw a triangle, square, pentagon, hexagon, etc.

180 (N-2) = 3780

N-2 = 3780/180

N-2 = 21

N= 23