Unit circle
The unit circle is the circle of radius 1 centered at the origin (0, 0). In this circle, the use of radians is preferred over the use of degrees.
Degrees
If the argument to sine is scaled by a frequency x, like in
then the first derivative gives
The second derivative shows
Radians
If this same sine is expressed in radians you get a different solution
Circular functions only behave correctly when radians are used.