### Radian system of measuring angles

All of the built-in trigonometric functions in FreeBASIC express angles in radians.

Let pi the 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 by 4.

A full circle is divided into 2 * pi radians or 360 degrees, which leads to the following conversions:

pi = atn(1) * 4 radians = degrees * pi / 180 degrees = radians * 180 / pi

These 3 formulas can be expressed by using macros:

#define pi ( atn(1) * 4 ) #define radian(x) ( (x) * pi / 180 ) #define degree(x) ( (x) * 180 / pi )

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