Trigonometric Identities

Links to Activity

Main Concepts

Matrix multiplication

Rotation matrix in the plane

Trigonometric identities


20 minutes

Summary of Activity

The sum and difference formulas for trigonometric functions can be elegantly proven using rotation matrices and some matrix multiplication. Matrix multiplication is defined to correspond to the composition of the two transformations.

Notes and Insights

This task can also be handed out to students in Precalculus, even though their understanding of matrix multiplication is mostly computational.