What is "in the regular nonagon shown?

A regular nonagon is a polygon with nine sides of equal length and nine angles of equal measure. In the regular nonagon, all the interior angles measure 140 degrees and all the exterior angles measure 40 degrees. The sum of the interior angles of any polygon is given by the formula (n-2) * 180, where n is the number of sides, so in the regular nonagon, the sum of the interior angles is (9-2) *180 = 1260 degrees. The regular nonagon can be tessellated, meaning that it can be used to cover a flat surface with no overlaps or gaps.