>>5101092 (pb, latest Q post)
What's with 30, 45, 60, 90, the first 4 lines of Q's post?
They are the angles of triangles we learn in trigonometry. You really don't do much but 30-60-90 and 45-45-90 right triangles, because the sines and cosines of those angles are simple and well known.
There's no 15 or 75 which would be in sequence if you were just going up by 15's . Those aren't typical angles used in learning trigonometry.