Atan-func
The atan(x) function returns the inverse of the corresponding trigonometric function. x can be any value for atan. Returned values are in radians, degrees or gradians, depending upon the system.math.angularunits object property (which can also be set in the Options dialog box).
double atan(double x)
x
Returns arctangent of x.
aa = atan(10); aa = ; //1.4711276743037
asin, acos, acot, asec, acsc