atan, atanf, atanl - arc tangent function

Syntax	#include <math.h> double atan(double x); C11 float atanf(float x); long double atanl(long double x); (End)
Description	These functions are the inverse function of the corresponding tan()-functions. They return the principal value (i.e. corresponding angle in radians) of the arc tangent of a floating-point number x .
Return val.	arc tangent(x) if successful. A floating-point number of type double in the range [-pi/2, +pi/2] is returned.
See also	acos(), asin(), atan2(), cos(), sin(), tan(), math.h.