Problem 307. Regular Nonagon or Enneagon, Midpoints, Side, Arc, Angle.
Level: High School, SAT Prep, College geometry.
In a regular nonagon ABCDEFGHI inscribed in the circle of center O, M is the midpoint of arc AB, N is the
midpoint of side BC and P is the midpoint of OM. Prove that the measure
of angle ONP is 30 degrees.