Question

Difficulty: EasyAngles, Parallel Lines, and Polygons

What is the measure, in degrees, of each interior angle of a regular octagon (an 8-sided regular polygon)?

Answer: 135 degrees

Answer

Each interior angle of a regular octagon measures 135 degrees.
The sum of the interior angles of a polygon with nn sides is (n2)×180(n - 2) \times 180^\circ. For a regular octagon (n=8n = 8), the total interior angle sum is (82)×180=1080(8 - 2) \times 180^\circ = 1080^\circ. Since all 8 interior angles of a regular octagon are congruent, dividing the total sum by 8 yields 135135^\circ for each interior angle.

Step-by-Step Solution

1
Find the sum of all interior angles of the regular octagon.
Sum of interior angles = (82)×180=6×180=1080(8 - 2) \times 180^\circ = 6 \times 180^\circ = 1080^\circ.
The sum of interior angles for any nn-sided polygon is (n2)×180(n - 2) \times 180^\circ.
2
Calculate the measure of a single interior angle.
Interior angle = 10808=135\frac{1080^\circ}{8} = 135^\circ.
In a regular polygon, all interior angles are equal in measure.

Key Concept

Interior Angle of a Regular Polygon
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