Respuesta :

[tex]\begin{gathered} x=\frac{\pi}{3} \\ \\ \cos (\pi+x)=cos(\pi+\frac{\pi}{3})=\cos (\frac{4\pi}{3}) \end{gathered}[/tex]

Using the unit circle above you can identify the cosine as the x-coordinate.

Then, the cosine of (4pi/3) is -1/2

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