Diagonals of Polygons
A polygon's diagonals are line segments from one corner to another, but not the sides.
The number of diagonals of an n-sided polygon is:
n(n - 3) / 2
- a square has 4(4-3)/2 = 4×1/2 = 2 diagonals
- an octagon has 8(8-3)/2 = 8×5/2 = 20 diagonals.
A triangle has no diagonals.
Try it Yourself:
|A diagonal can actually be outside the polygon,
which happens with some concave polygons.