This gives (10 – 2) × 180 = 1440 Image caption, Find the sum of the interior angles of a 26-sided polygon. It would not be practical to draw a 26-sided polygon, so the formula is more useful here.

By doubling the number of sides of the hexagon to a 12-sided polygon, then a 24-sided polygon, and finally 48- and 96-sided polygons, Archimedes was able to bring the two perimeters ever closer in ...