25.4.3 Periodicity and Even/Odd Symmetry
Core ideaThe wave repeats after a fixed stretch — that stretch is the period — and symmetry about the origin makes it odd, while symmetry about the y-axis makes it even.
Module goal. We 'unroll' the turning of a point on the unit circle into a wavy curve, getting a firm grip on period, even/odd symmetry, increasing/decreasing behavior, and extremes, to lay the groundwork for parameter transformations and the laws of sines and cosines.