1. The problem statement, all variables and given/known data Solve for x using half-angle identities cos (x/2) = -√2 / 2 2. Relevant equations cos(x/2) = ± √(1+cosx)/2 3. The attempt at a solution I am trying to figure out what to do with the identity, but I have no idea how to start. I know that x = 270 degrees or 3pi/2, but I do not know how to get there. Can someone head me in the right direction?