25.4.2 Graphs and Properties of Sine and Cosine
Core ideaThe two waves are just shifted sideways by a quarter period from each other, both repeat every 2π, and both stay between -1 and 1.
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.