Precalculus

Lecture 21: The Unit Circle: Defining the Sine and Cosine Functions

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There are different ways to define the sine and cosine functions. We choose to define them in terms of the unit circle, which is the circle having center at (0,0) and radius 1.

This lecture borrowed several images from the OpenStax Precalculus book. The graphics that appear on Slides 8, 9, and 13 come from Section 5.2 of that book (accessible for free). Excerpts from Precalculus are allowed under the Creative Commons Attribution 4.0 International License.