First, let's calculate the value of cos 2pi/3:
[tex]\cos\frac{2\pi}{3}=-0.5[/tex]
Now, let's calculate the value of each option:
[tex]\begin{gathered} \cos\frac{\pi}{6}=0.866\\ \\ \\ \\ \cos\frac{4\pi}{3}=-0.5\\ \\ \\ \\ \sin\frac{5\pi}{3}=-0.866\\ \\ \\ \\ \sin\frac{7\pi}{6}=-0.5\\ \\ \\ \\ \cos\frac{11\pi}{6}=0.866 \end{gathered}[/tex]
Therefore the correct options are B and D.
