Internal and external angle
From Wikipedia, the free encyclopedia
In geometry, an interior angle (or internal angle) is an angle formed by two sides of a simple polygon that share an endpoint in. This angle must be an angle on the inner side of the polygon to be an internal angle. A simple polygon has exactly one internal angle per vertex.
If every internal angle of a 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.
The sum of the internal angle and the external angle on the same vertex is 180°.
For example: x+35+75=180
x+110=180
x+110-110=180-110
x=70
The sum of all the internal angles of a Regular polygon can be determined by 180(n-2) where n is the number of sides. A pentagon's internal angles add up to of 540 degrees (shown below)
180(n − 2) = 180(5 − 2) = 180(3) = 540
Knowing this you can easily find the measure of each angle (assuming those angles are part of a regular polygon) with
.
So continuing from the above example with the pentagon...
