Definition:Polygon/External Angle
< Definition:Polygon(Redirected from Definition:Exterior Angle of Polygon)
Jump to navigation
Jump to search
Definition
Contrary to intuition, the external angle of a vertex of a polygon is not the size of the angle between the sides forming that vertex, as measured outside the polygon.
An external angle is in fact an angle formed by one side of a polygon and a line produced from an adjacent side.
While $\angle AFE$ is the internal angle of vertex $F$, the external angle of this vertex is $\angle EFG$.
Also known as
An external angle is also known as an exterior angle.
Also see
- Vertical Angle Theorem, which shows that it does not matter which adjacent side you use, because they are equal.
- Results about external angles can be found here.
Sources
- 1998: David Nelson: The Penguin Dictionary of Mathematics (2nd ed.) ... (previous) ... (next): exterior angle: 1.
- 1998: David Nelson: The Penguin Dictionary of Mathematics (2nd ed.) ... (previous) ... (next): external angle
- 2008: David Nelson: The Penguin Dictionary of Mathematics (4th ed.) ... (previous) ... (next): exterior angle: 1.
- 2008: David Nelson: The Penguin Dictionary of Mathematics (4th ed.) ... (previous) ... (next): external angle
- 2014: Christopher Clapham and James Nicholson: The Concise Oxford Dictionary of Mathematics (5th ed.) ... (previous) ... (next): polygon
- 2021: Richard Earl and James Nicholson: The Concise Oxford Dictionary of Mathematics (6th ed.) ... (previous) ... (next): polygon