Google is your friend: Be nice and visit him often. He can answer questions a lot more quickly than posting them here...
A very quick search
using your subject as the search term gave 16 million hits:
Google[
^]
The top hit gives a full solution with an explanation.
http://in.answers.yahoo.com/question/index?qid=20090518062006AAWCsaT[
^]
In future, please try to do at least basic research yourself, and not waste your time or ours.