Stuck on a exm revision question please help, the question is:

Find the exact value of:

a) cos(x) if sin(x) =12/13 and 90°<x<180°

b) sin(x) if cos(x) =-3/2 and x is in the third quadrant

c) cos(x) if sin(x) =-7/25 and x is in the fourth quadrant

d) sin(x) if cos(x) = (root 3)/2 and 3pi/2<x<2pi

thnx i dont know how t use ths very well i hope you understand what i mean