Glencoe Math: Course 3, Volume 2
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Glencoe Math: Course 3, Volume 2 View details
4. Polygons and Angles
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Exercise 24 Page 403

In a polygon, the sum of the measures of the exterior angles — one at each vertex — is 360^(∘).

30^(∘)

Practice makes perfect

To find the measure of an exterior angle of a regular 12-gon, we will first recall an important piece of information.

Exterior Angles of a Polygon

In a polygon, the sum of the measures of the exterior angles — one at each vertex — is 360^(∘).

This means that the sum of the exterior angles of a regular 12-gon is also 360^(∘). A 12-gon has 12 vertices and 12 exterior angles.

Regular polygon with exterior angles

In a regular polygon, all exterior angles are congruent. Therefore, a regular 12-gon has 12 congruent exterior angles. To find the measure of one of them, we will divide 360^(∘) by 12. 360/12 = 30^(∘)