Question

Given x = pi/3, what is the exact value of cos (pi+x)?

Answer 1

`\begin{gathered} x=(\pi)/(3) \\ \\ \cos (\pi+x)=cos(\pi+(\pi)/(3))=\cos ((4\pi)/(3)) \end{gathered}`

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

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