What is it? A circle is a shape consisting of points — in the same plane — that are equidistant from a center point.
Radius (r): Distance from any point on the circle to the Center (c)
Diameter (d): Length of any line segment that connects two points on the circle AND passes through the center
Diameter = 2 x Radius
The center is the midpoint of any diameter.
Area of the circle: π (radius)² = π r²
Circumference: the “perimeter” of the circle: π (diameter) = π d
or 2 π (radius) = 2 π r
π is an irrational number approximately 3,1415
Example: Given a circle with radius 6 inches
area = π r² = π (6 inches)² = 36 π square inches
(approximately 113.1 sq. inches)
circumference = π d = π (12 inches) = 12 π inches
(approximately 37.7 inches)