1. The problem statement, all variables and given/known data cos(x - 3p/2) = - 4/5 p <x< p/2 sin(x/2)*cos(5p/4)= ? 2. Relevant equations 3. The attempt at a solution I made it as far as to determine that sinx= 4/5 and cosx = - 3/5 but cant seems to progress any further. Im looking for an easier way to find the solution without having to deal with halfangle roots and all of that. Any hints?