The question wants me to find sin(x/2) when cosx = -(12/13) in the interval (pi,3pi/2). I know that the eventual answer will be 5/sqrt26, however, I am not sure how to get there.

Answer 1

the interval is Quad III , so x/2 will be in Quad II

sin(Θ/2) = ± √{[1 - cos(Θ)] / 2}