Circle

Math

A circle is a polygon which is a round object, which means it has no Schläfli symbol.

The circle is the most common use of the constant pi, which is also seen in the diagram itself.

Measurements
The area of a circle is \(\pi r^2\).

The circumference of a circle, which pi is defined from, is \({\pi}d\).

Other similar shapes
There are other shapes derived from a circle.

Half a circle
Half a circle is also called a semicircle. It is made from an arc which is half a circle and a straight line joining the ends of the arc, forming a polygon.

Quarter of a circle
Quarter of a circle is called a quadrant, or a quarter-circle. It is made from an arc which is a quarter of a circle and 2 straight lines joining the ends of the arc, forming a quadrant.

Others
There are others based on fractions of a circle, like sextants (\(\frac16\)) and octants (\(\frac18\)).