An exterior angle β of a polygon is the angle formed externally between two adjacent sides. It is therefore equal to 2π - α, where α is the corresponding internal angle between two adjacent sides. Consider the angles γ_i formed between a side of a polygon and the extension of an adjacent side. Since there are two directions in which a side can be extended, there are two such angles at each vertex. However, since corresponding angles are opposite, they are also equal. Confusingly, a bisector of an angle γ is known as an exterior angle bisector, while a bisector of an angle β (which is simply a line oriented in the opposite direction as the interior angle bisector) is not given any special name.
We guarantee you’ll find the right tutor, or we’ll cover the first hour of your lesson.