n Interior Degrees Degrees at a vertex 3 180 60 4 360 90 5 540 108 6 720 120 7 900 128.57 8 1080 135
Let one of the exterior angles be E
Then one of the interior angles is: 3E
Since the exterior and interior angles are supplementary, we get: E + 3E = 180
4E = 180
E, or one of the EXTERIOR angles =, or 45o
Since the exterior angles of any polygon sum to 360o, we can say that the number of sides of the polygon =, or , thus making it an OCTAGON.