Use the exterior angle to calculate the number of sides for each regular polygon
Home / 8th grade / Geometry & measures / Polygons / Number of sides from exterior angle
The exterior angle of a polygon is the angle made by one side of the polygon and the extension of the next side of the polygon. By applying the angles on a straight line rule, we know that the interior angle plus the exterior angle sum to 180°. The sum of the exterior angles of polygons is always 360°.
This topic deals with regular polygons. Regular polygons have equal length sides and each of their interior angles is identical. Examples of regular polygons are equilateral triangle, square, regular hexagon, etc. Because their interior angles are identical, their exterior angles are also identical. The formula for calculating the number of sides of a regular polygon given it's exterior angle is:
Number of sides = 360° / E
(where 360° = total of exterior angles and E = exterior angle of polygon)
So, for a regular polygon with an exterior angle of 120°, the number of sides is:
360° / 120° = 3
For a regular polygon with an exterior angle of 90°, the number of sides is:
360° / 90° = 4
For a regular polygon with an exterior angle of 72°, the number of sides is:
360° / 72° = 5
Below is a table showing the first 6 question answer pairs for the topic "Number of sides from exterior angle" as used in the lessons for this topic. Our games and tests for the topic use these 6 items plus 10 additional question answer pairs.
The topic "Number of sides from exterior angle" is in the category Geometry & measures for 8th grade (ages 13 to 14).
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