Format

      #include  <math.h>

      double atan  (double x);

      float atanf  (float x); (Integrity servers, Alpha)

      long double atanl  (long double x); (Integrity servers, Alpha)

      double atand  (double x); (Integrity servers, Alpha)

      float atandf  (float x); (Integrity servers, Alpha)

      long double atandl  (long double x);

                          (Integrity servers, Alpha)