------->whose=det.pronoun; is used to say which person you mean;eg:-He s a man whose opinion I respect.
Don t use his/her to begin unless to follow;
Don t use the comma when whose not follow the subject;
To copy exactly your wording:-?:-
-------->Mr. Lin was my math teacher in my college whose unique teaching method impressed me a lot.
------->Or:-Mr.Lin, whose unique teaching method impressed me a lot, was my math(s) teacher in my college.(useing double commas)