Hi, I Know what to do, find the first derivative. But i get stuck on a line which can't find the exact value.

Question: Find the gradient of the tangent to the curve y = 3cos2x at the point where x = pi/6.

dy/dx = -6sin2x

y'(pi/6) = -6sin(2*pi/6)

=-6sin(2pi/6)

how do I simplify that? I'm totally lost as of what to do next.

PS: On another note what does d/dx mean as compared to dy/dx?

Thanks,

MBB