This lesson marks the beginning of a transition for students and their thinking about periodic functions. In this lesson, we define a periodic function to include any function in which the output values repeat at regular intervals, and we show that the graphs of these types of functions can have a wave-like appearance.

During this lesson, students have the opportunity to reason abstractly and quantitatively about graphs of situations that have repeated behavior (MP2). Then they categorize graphs of functions in order to compare periodic with non-periodic functions and communicate their observations about graphs precisely with others (MP6).