All of the built-in trigonometric functions in FreeBASIC express angles in radians.
A full circle is divided into 2 * pi radians or 360 degrees, which leads to the following conversions:
radians = degrees * pi / 180
degrees = radians * 180 / pi
Pi is a constant equal to the ratio of the circumference of a circle to its diameter. It can be calculated programmatically by multiplying the arctangent of 1 radian by 4:
pi = atn(1) * 4