warm-up what is the perimeter of a regular decagon with side length s = 6?
TRANSCRIPT
Warm-Up
• What is the perimeter of a regular decagon with side length s = 6?
Geometry 9-2
Developing Formulas for Circles and Regular Polygons
DefinitionsA circle is the collection of points in a plane that are a fixed distance from a point called the center of the circle. A circle is named by the symbol and its center. A has radius r = AB and diameter d = CD.
Circumference and Area
Example
Find the area and circumference of K.
Example
• What is the area of the shaded region?
mCBA = 60.00
C
B
A
4 in.
DefinitionThe center of a regular polygon is equidistant
from the vertices. The apothem is the distance
from the center to a side.
The apothem of the figure is BC.
Formula
Examples
• What is the area of a regular triangle with side length s = 4m and apothem a = 1.5m.
• What is the area of a regular octagon with side length s = 5 and apothem a = 2.