Returns a double value that is the tangent of its radian
    argument.

    Format

      #include  <math.h>

      double tan  (double x);

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

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

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

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

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