Radian system of measuring angles
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