This video presents the formula for the sum of the interior angles of a polygon.
Source: RobertOB on Guaranteach
This video presents the fact that the sum of the exterior angles of any polygon is 360 degrees.
Source: RobertOB on Guaranteach
This video explains how to find an unknown angle using the formula for the sum of the interior angles of a polygon.
Source: RobertOB on Guaranteach