Polygon's interior and exterior angle
A polygon always has an exterior angle sum to 360 no matter the number of sides or their width.
A triangle has an exterior angle sum equal to 360
A square has an exterior angle sum equal to 360
A pentagon has an exterior angle sum equal to 360
Quadrilaterals have exterior angle sum equal to 360
There's a pattern.
All of the above shapes are polygons, and polygons could have n-sides or n-angles.
To find the sum of interior angles for these polygons, we just subtract the exterior angle sum from the interior
a + b + ... aN = N * 180 - 360
where a, b .. N are interior angles.
N is number of angles in the polygon.