Hands-on math!

The Circle

A circle is a plane figure in which all points on it are the same distance from the center.

The RADIUS R is the distance from the center to the edge.

The DIAMETER D is the distance across the circle.

The CIRCUMFERENCE C is the distance around the edge of the circle.
It's the perimeter of the circle.
The diameter D is twice the radius R or

D = 2 R

The circumference C is ("pi") times the diameter D

C = D

is 3.1415926...(goes on forever), but just use 3.14 for

The area A of a circle is:
A = R x R or ...
A = R2

So, for a circle whose radius R is 6 inches:
  • The diameter D = 2 R = _________
  • The circumference C = D = _________
  • The area A = R x R = ________