SOLUTION
The given value is:
[tex]x=\frac{\pi}{3}[/tex]It follows that:
[tex]\cos(\pi+x)=\cos(\pi+\frac{\pi}{3})[/tex]This gives:
[tex]\begin{gathered} \cos(\pi+\frac{\pi}{3}) \\ =\cos(\frac{3\pi+\pi}{3}) \\ =\cos(\frac{4\pi}{3}) \\ =-\frac{1}{2} \end{gathered}[/tex]Therefore the correct answer is option D
