If z=cos(2π/9)+isin(2π/9)z = \cos(2\pi/9) + i\sin(2\pi/9)z=cos(2π/9)+isin(2π/9), what is the value of z3+z−3z^3 + z^{-3}z3+z−3?
2\cos(2\pi/3)
-1
0
1