For reasons that have to do with calculus, the further you go with mathematics the more sense it makes to measure angles not in degrees but in radians. There are 2\pi radians in a full circle. It's worth committing the following table to memory:
| degrees | radians |
| 0 | 0 |
| 30 | \pi/6 |
| 45 | \pi/4 |
| 60 | \pi/3 |
| 90 | \pi/2 |
| 180 | \pi |
| 270 | 3\pi/2 |
| 360 | 2\pi |