Education Technology

Precalculus: Radian Measure

by Texas Instruments


  • Students will describe the relationship between a central angle, the radius, and the arc length of a circle.
  • Students will recognize that changing the radius of a circle does not affect the proportions in the circle.
  • Students will convert an angle measure from radians to degrees and vice versa.


  • central angle
  • exact value
  • radian
  • right angle

About the Lesson

This lesson involves exploring the relationship between the central angle, the arc, and the radius of a circle.
As a result, students will:

  • Use a slider to change the radius, and conclude that the relationships are preserved.
  • Form a definition of a radian.
  • Drag a point to change the measure of the central angle to discover the relationship between radian and degree measure.
  • Create a proportion that can be used to convert the measure of an angle from degrees to radians and vice versa.