# Circle Formulas

A circle is a shape consisting of all points in a plane that are at a given distance from a given point, the centre.

Radius is the distance between any point of the circle and the centre.

Diameter is a straight line segment whose endpoints lie on the circle and that passes through the centre.

## Circumference of a circle

$$C=2 \times \pi \times r= \pi \times d$$

where,

π— pi or Archimedes's constant is a mathematical constant, that is a ratio of a circle's circumference to its diameter, approximately equal to 3.14159265359;
$$S=\pi \times r^{2}=\frac{\pi \times d^{2}}{4}$$