The purpose of this lesson is for students to extend their understanding of cosine and sine from ratios of right triangles, or the - and -coordinates of points on a unit circle for a specific angle, to functions that have an angle measure as an input. Building on their earlier work studying the structure of the unit circle, students plot points for the graphs of and for values of from 0 to radians (MP7). Students also use technology to graph several trigonometric functions, including , recalling earlier work with the Pythagorean Identity.

In future lessons, students will build on this work to create new functions, based on cosine and sine, that model periodic motion, such as the height of the blade of a windmill or how the amount of the face of the moon that is illuminated changes over the course of a lunar month.