Question

Given x=pi/3, what is the exact value of cos(pi+x)?A. 1/2B. - square root of 3/2C. square root of 3/2D. -1/2

Answer 1

The given value is:

`x=(\pi)/(3)`

It follows that:

`\cos(\pi+x)=\cos(\pi+(\pi)/(3))`

This gives:

`\begin{gathered} \cos(\pi+(\pi)/(3)) \\ =\cos((3\pi+\pi)/(3)) \\ =\cos((4\pi)/(3)) \\ =-(1)/(2) \end{gathered}`

Therefore the correct answer is option D