Hi,

I'm working with a question that I think mainly involves trig identities, but I'm not sure if I have the right approach and can't figure out the later parts.

I'm also not sure how it being in the third quadrant plays a role...If cos(x)=-5/7 where pi < x < 3pi/2, find the values of cos(2x), sin(2x), cos(x/2), sin(x/2)

For the first two, I worked out that cos(2x)=1/49 and sin(2x)=4sqrt6/7 with double angle formulas, but I'm not sure if those are correct and I don't know where to go now.

Thanks!