Interior and Exterior Angles of a Polygon

Mathematics — Second Preparatory

Common mistakes

Using (n − 2) × 180 without subtracting 2 from the number of sides, which gives a wrong sum.
Thinking the sum of the exterior angles equals (n − 2) × 180. In fact it is always 360°.
Dividing the sum of the interior angles by the number of sides in an irregular polygon. This gives an average, not a specific angle.
Forgetting that an exterior angle of a triangle equals the sum of the two opposite interior angles, not the two adjacent ones.

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