code: function() {
  
        // acos(c) = i * log(c - i * sqrt(1 - c^2))
  
        var a = this['re'];
        var b = this['im'];
  
        var t1 = new Complex(
                b * b - a * a + 1,
                -2 * a * b)['sqrt']();
  
        var t2 = new Complex(
                t1['re'] - b,
                t1['im'] + a)['log']();
  
        return new Complex(Math.PI / 2 - t2['im'], t2['re']);
      }
docs: Calculate the complex arcus cosinus
  
  @returns {Complex}