"unit circle"
Ahhh, the Unit Circle.
Pure simplicity covering Sine and Cosine bouncing from 1 to -1, producing trig tables and x-y projections. Adds a nice mechanic to all of those 90 degree out of phase signals.
If you haven't used it your missing out!
"Trigonometry is essentially a procedure for turning angular measures into linear measures." --Saunders Mac Lane