In the figure below, angle BDE is an exterior angle of polygon ABCD. It is formed by side BD and the extension of side CD.
- The sum of the degree measures of the exterior angles of a convex polygon is always equal to 360°.
- The measure of an exterior angle of a triangle is equal to the sum of the measures of the remote interior angles of the triangle.
In the figure shown above, the measure of the exterior angle at vertex C is equal to the sum of the measures of the remote interior angles at vertices A and B.