Internal and external angles
Internal and external angles
An angle of a polygon is formed by two sides of the polygon that share an endpoint. For a simple (non-self-intersecting) polygon, regardless of whether it is convex or non-convex, this angle is called an interior angle (or internal angle) if a point within the angle is in the interior of the polygon. A polygon has exactly one internal angle per vertex.
If every internal angle of a simple polygon is less than 180°, the polygon is called convex.
In contrast, an exterior angle (or external angle) is an angle formed by one side of a simple polygon and a line extended from an adjacent side.
Video: What is the Relation of an Exterior Angle of a Triangle with its Interior Angles?
Properties
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The sum of the internal angle and the external angle on the same vertex is 180°.
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The sum of all the internal angles of a simple polygon is 180(n–2)° where ......
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