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Angles in a polygon

Exterior angles of any polygon add to 360°. In a regular polygon they are equal, and each interior angle makes 180° with the exterior angle at the same vertex. For a triangle on its own, use angles in a triangle. For a transversal, use angles in parallel lines.

Regular polygon with one interior angle and one exterior angle.IENot to scale.
A regular hexagon is shown. The red label is an interior angle. The dashed line is the side extended, so you can see the exterior angle. Your polygon may have a different number of sides.

Use 3 to 100 sides. An exterior angle must divide 360° exactly, and it is at most 120°.