Education Technology

Precalculus: Proof of Identities

by Texas Instruments


  • Students will be able to interpret reciprocal, negative angle, cofunction, and Pythagorean identities in terms of the graphs of the trigonometric functions involved.
  • Students will be able to prove trigonometric identities algebraically.
  • Students will be able to visualize trigonometric identities graphically.


  • Cofunction Identities
  • Identity
  • Negative Angle Identities
  • Pythagorean Identities
  • Reciprocal Identities
  • Trigonometric Identities

About the Lesson

This lesson involves discovering, visualizing, and proving trigonometric identities.
As a result, students will:

  • Manipulate the graphs of trigonometric functions.
  • Utilize sliders to discover and support trigonometric identities.
  • Drag a point to see its relationship to its reflected image and use this information to discover the Negative Angle Identities.
  • Utilize the relationship between an angle and its complement to discover the Cofunction Identities.