The term exterior angle of a polygon is used in two related senses. Most commonly, an exterior angle 
is the angle between a side and the extension of an adjacent
side. For a convex polygon, it is supplementary
to the corresponding interior angle 
, so
 |
Since either side can be extended, there are two such exterior angles at each vertex. These angles are vertical angles and therefore equal.
Alternatively, exterior angle may denote the reflex angle 
between two adjacent sides that lies
outside the polygon. In this convention,
 |
(Zwillinger 1995, p. 270).
A bisector of an angle 
is known as an exterior angle bisector,
while a bisector of an angle 
(which is simply a line oriented in the opposite direction
as the interior angle bisector) is not given any
special name.
The sum of the angles 
in a convex polygon is equal to 
radians (
), since this corresponds to one complete rotation
of the polygon.
