25.4.4 Intervals of Increase/Decrease and Extremes
Core ideaBetween a crest and a trough the curve climbs or falls the whole way, with crests being maximums and troughs being minimums.
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.