Answer
The derivative is $-\pi*sin(t)$
Work Step by Step
This derivative requires you to remember two things:
1) The derivative of cos(t) is -sin(t).
2) $\pi$ is a constant and so doesn't affect the differentiation whatsoever.
Hence the derivative is $\pi *\frac{d}{dt}cost$ which is $-\pi*sin(t)$
