Circles and PiRadians

Radians

Rather than dividing a circle into some number of segments (like 360 degrees), mathematicians often prefer to measure angles using the circumference of a unit circle (a circle with radius 1).

A has circumference .

For a , the corresponding distance along the circumference is .

For a , the distance along the circumference is .

And so on: this way of measuring angles is called radians (you could remember this as “radius units”).