find exact value

[magmagod]

if sin(x) = (-4/5), then find the exact value of the following:

a. tan(x)
b. sin(2x)

this is what i did to b.

2 sinx cosx
2 (-4/5)(3/5)
2(-12/25)
-24/25

i got cos x by the pyth theorm (x^2+y^2=r^2)

im really confused cause it says it might have two answers and what not..so please help