The Unit Circle – Part I establishes the connection between angles measured counterclockwise from the positive side of the x-axis and points on a circle of radius 1 and formalizes this as a function from angles to points (ordered pairs). From this, the sin and cos functions are defined. Value of sin and cos are found for angles which are multiples of 90°. Values which come from the 30° – 60° – 90° triangle and the 45° – 45° – 90° triangle are presented in the Unit Circle – Part II lesson.
Precalculus by Mike Weimerskirch and the University of Minnesota Board of Regents is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License, except where otherwise noted.