Section 11.6 Notes
Regular Polygon and its Parts
A regular polygon is an equilateral and equiangular polygon. E C D BA
The center of a regular polygon is the center of the circumscribed circle. Pt. O is the center of regular pentagon ABCDE. A B E C D O
The radius of a regular polygon is a segment connecting its center with a vertex. A B E C D O
How many radii does a regular pentagon have? 5 radii How many radii will any regular polygon have? The number of sides
An apothem of a regular polygon is the distance from the center to the side of the regular polygon. A B E C D O F
A central angle of a regular polygon is an angle whose vertex is the center of the polygon and whose sides contains consecutive vertices of the polygon. A B E C D O
1.Draw a regular triangle, a regular quadrilateral, and a regular hexagon. 2.Draw all the central angles of each of the regular polygons. 3.What must be true of all central angles of a regular polygon and what is the sum of these angles? They are congruent. Their sum is 360 .
4.Find the measure of one central angle of each of the regular polygons from #1. regular triangle is 120° regular quadrilateral is 90° regular hexagon is 60°
5.Find measure of one central angle of a regular n-gon.
Example 1 Find the measure of a central angle of the following regular polygons: a)a regular pentagon
c)a regular 20-gon b)a regular octagon
Find the apothem and radius of each of the following regular polygons. Example 2
1.a regular triangle with a side length of a r 30 60 6
2.a regular quadrilateral with a side length of a r 20 10
3.a regular hexagon with a side length of a r 8 4
Area of a Regular Polygon The area of a regular polygon is half the product of the apothem and the perimeter of the regular polygon.
A B E C D O a s
Example 3 Find the area of each of the following regular polygons. 1.a regular triangle with a side length of 18 in. 18 in. a 30 9
2.a regular quadrilateral with a side length of 12 ft. using the area of a regular polygon formula 45 a 12 ft. 6
3.a regular hexagon with a side length of 6 cm 60 a 6 cm. 3
Example 4 Find the area of a regular octagon with side length of 14 cm to the nearest centimeter. 14 cm a
Example 5 Find the area of a regular pentagon with side length of 12 cm. to the nearest hundredth. a 12 cm