The asec(x) function returns the inverse of the corresponding trigonometric function sec(x)=1/cos(x). Absolute value of x must greater than or equal to 1 for asec, or a missing value is returned. Values returned are in the first or second quadrant in units of radians, degree or gradian. The units are determined by the system.math.angularunits object property (which can also be set in the Options dialog box).
double asec(double x)
Returns the arcsecant of x.
aa = asec(1); aa = ; //should return 0
Asin, Acos, Acsc, Atan, Acot