## Trigonometry teachers HATE HIM

Somewhere in my years of “tutoring calculus,” also sometimes referred to as “tutoring trigonometry,” I discovered a trick (here meaning a tool devoid of any conceptual knowledge of the topic at all) for evaluating the cosine (and therefore also sine) of the upper-right quadrant special angles $0, \pi/6, \pi/4, \pi/3, \pi/2$. This can be extended to the rest of the unit circle in the usual way.