Pre-calc Trig Help!

[gabriellelizz]

Please help me answer this problem with work... Thanks so much in advance!
Given sin (theta) = -4/5, where 3*pi/2 < or equal to 0 < 2*pi, find the exact value for tan 2 (theta)

 

[topsquark]

As you haven't said where you are having trouble let me start you off with a diagram:


(I have used the reference angle here.)

Can you find $$\tan ( \theta )$$ from this? Once you have that, how do you find $$tan(2 \theta )$$?

-Dan