Circle ○

A circle is a basic shape consisting of the points at a given distance from a given point on a plane.

Definitions:
  • r: Radius
  • d: Diameter
  • U: Circumference
  • A: Area
r U d U

Circumference of a Circle

The circumference U is the distance around a closed curve.

\(U=2*Pi*r\)
U = Circumference
r = Radius
\(r=U/(2*Pi)\)
r = Radius
U = Circumference
\(U=Pi*d\)
U = Circumference
d = Diameter
\(d=U/Pi\)
d = Diameter
U = Circumference

A r A d

Area of a Circle

The region inside a circle.

\(A=Pi*r^2\)
A = Area
r = Radius
\(r=sqrt(A/Pi)\)
r = Radius
A = Area
\(A=Pi/4*d^2\)
A = Area
d = Diameter
\(d=sqrt(4*A/Pi)\)
d = Diameter
A = Area