The arcsine of a number is the angle whose sine is that number. ASN returns a value between ±PI/2 radians or ±90 degrees. The default trigonometric mode is radians unless changed with the DEG statement. Its argument must be a value between -1 and 1 inclusive.
COMPLEX Arguments
ASN accepts either a COMPLEX or REAL argument and returns a value of the same type. For COMPLEX arguments the angle is returned in radians, regardless of the current trigonometric mode. ASN returns the principal value, defined (in terms of complex arithmetic) as
which returns a real part in the range -PI/2 to PI/2. The domain for COMPLEX arguments includes all points in the complex plane (but for REAL arguments, the domain is still -1 to 1, inclusive). Notice that intermediate values generated during the calculation of the function can cause over or underflow errors for very large or small values of Z.
