Education Technology

Precalculus: The Unit Circle

by Texas Instruments


  • Students will describe the relationship between the unit circle and the sine and cosine functions.
  • Students will describe the shape of the sine and cosine curves after unwrapping the unit circle.


  • continuous function
  • periodic function
  • unit circle

About the Lesson

This lesson involves using a slider to change the measure of the central angle of a unit circle and making connections with right triangle trigonometry.
As a result, students will:

  • Discover the relationships between the right triangle and the line segments creating the sine and cosine functions.
  • Observe that as the measure of the central angle changes line segments representing the length of a highlighted leg of the right triangle in the unit circle appear on the screen.
  • Need prerequisite knowledge of right triangle trigonometry and continuous functions.