# Circular System

## Circular System

Name given to the system for measuring angles in which the base unit is the radian.

This system of measurement is called the circular system because of the association between the definition of the radian and the circle. In trigonometry, we most often use measures of angles expressed in radians.

### Properties

In this system of measurement, the angle corresponding to a complete circle with radius r measures 2π radians and the circumference of this circle is given by C = 2πr.