(Lecture: 10 minutes)

• Trig functions are coordinates on unit circle.
• Angles measure (scaled) arclength.

Based on §3 of the text, especially §3.2.

Having just given students a chance to reflect on the essential ideas of circle trigonometry (in this SWBQ), this is an opportunity to reinforce the geometry of trig with a clear, unifying lecture. The order is important: this is circle trig, not (yet) triangle trig; the trig functions are defined as coordinates on the unit circle, not as ratios.