tan function
Return the tangent of complex.
Implementation
Complex<num, num> tan(Complex complex) {
var base = math.cos(2 * complex.real) + _cosh(2 * complex.imaginary);
var r = math.sin(2 * complex.real) / base;
var i = _sinh(2 * complex.imaginary) / base;
return Complex<num, num>(r, i);
}