Quote Originally Posted by Oddo
Четверг восемнадцатый декабря
In case of somebody will have to pronounce it, word «восемнадцатый» is an adjective of neutral noun «число» and it must be put in neutral gender (here it stands in masculine). Proper spelling is «Четверг, восемнадцатое декабря».

Татьяна has only one proper form «Татьяна». As far as I know in old times it was spelled like «Татиана»

Word «изучение» is an uncountable noun. It is used only in singular form (in most cases at least).