rayray; please note that you must start showing some work here in order for us to help you. Simply quoting an answer does not show what effort you have made, or even what you have done to get your answer. In this question for example, I have no idea what you have done to get your answer; but if you showed your work, I would probably be able to point out your mistakes.
As for the actual approach; I would take Defennnder's advice and try to recall how to integrate f'/f.