The exterior angles of a polygon add up to 360º in measure. For a regular heptagon, each exterior angle has an equal measure xº, so that 7xº = 360º, or xº ≈ 51.43º. Interior angles supplement exterior angles, so they each have measure 180º - xº ≈ 128.57º. Multiply this by 7 to get a total of 900º.
