The independent variables of trigonometric functions have units, which are degrees (°: Degree) and radians (Radian). The corresponding relationship between the two is very easy to remember. You only need to master the transformation formula 2π = 360° (a circular angle equals 360 degrees). From this formula, you can directly deduce that 30°= π/6, 45°= π/4, 60°= π/3, 90°= π/2, and so on.