trig problem...half-angle identities?

Question

if you could direct me with how to figure out the sine or cosine i'll be on my way to solving for the other trig functions. thanks in advance!

here's the problem.

find sin x and cos x given cos(x/2)= -1/4 and is in quadrant 2

Answer 1

cos (x/2) = +/- sqrt((1+cosx)/2)
-1/4 = +/- sqrt((1+cosx)/2)
1/16 = (1+cosx)/2
1/8 = 1 +cos x
cos x = -7/8
x = 151 .045 degrees
sin(151.045) = .4842