# Introduction to Radian Measure

- Author:
- Thomas Gebbie

1. Move the "Arc" slider so that the arc is the same length as the radius. How many degrees is the central angle that subtends (borders) the arc that is the same length as the radius?
Instead of saying that the angle formed by an arc the length of one radius is 57.3 , we say the angle measures one radian.
Radians are an alternate unit of measurement for angles. Instead of degrees, sometimes radians are used.
An angle measure of 1 radian is the angle subtended (cut out) by an arc on the circle that is exactly the length of 1 radius.
2. Describe what a radian is in your own words.
3. How many degrees are in a semi-circle?
4. How many radians are in a semi-circle?
5. How many degrees are in a full circle?
6. How many radians are in a full circle?
7. How many radians are in ¼ of a circle?