1. The problem statement, all variables and given/known data http://prikachi.com/images/26/4273026B.gif 2. Relevant equations 3. The attempt at a solution I'm having problems in solving the limit which is shown on the gif file . As you see I use L'Hopital's rule 2 times and I get to a point when I should divide -sinx with sinx which results in -1 instead of 1 which is the right answer according to the key. P.S sorry for posting the same thread in another sub-forum before I came here.