code: function(symbol) {
                                                                          var p = symbol.power,
                                                                              k = p/2, e;
                                                                          if(symbol.fname === COS)
                                                                              e = '((1/2)+(cos(2*('+symbol.args[0]+'))/2))^'+k;
                                                                          else
                                                                              e = '((1/2)-(cos(2*('+symbol.args[0]+'))/2))^'+k;
  
                                                                          return _.parse(e);
                                                                      }
docs: performs double angle transformation