# Classroom Activities

• ##### Subject Area

• Math: Precalculus: Trigonometry (Triangle and Circular Functions)

9-12

45 Minutes

• ##### Device
• TI-83 Plus Family
• TI-84 Plus
• TI-84 Plus Silver Edition
• TI-84 Plus C Silver Edition
• TI-84 Plus CE
• ##### Software

TI Connect™
TI Connect™ CE

• ##### Report an Issue

Trigonometric Identities

Published on 01/17/2011

#### Activity Overview

Students will verify, prove, and explore trigonometric identities symbolically, numerically, and graphically.

#### Key Steps

• Students will use the VERITRIG program to help prove the two trigonometric identities. They will use the Text tool to label a triangle drawn within the unit circle. Then students will write x and y in terms of cosθ and sinθ to prove the identity cos2θ + sin2θ = 1.

• Students then prove the identity sec2θ = 1 + tan2θ using similar triangles and ratios.

• After proving the identities, students can use the cosine and sine values of the angles in the unit circle to prove that the proof holds for each identity.