acos method
Arccosine
Compute the inverse cosine of this complex number.
Implements the formula:
acos(z) = -i (log(z + i (sqrt(1 - z^2))))
Returns nan
if either real or imaginary part of the
input argument is NaN
or infinite.
Implementation
Complex acos() {
if (isNaN) return Complex.nan;
return (this + (sqrt1z() * Complex.i)).log() * (-Complex.i);
}