Cannot find the derivative of a function in terms of time

So I have a function lets say B=a*cos(q), where a is a constant and q is an articulation angle.

Now to find the velocity I wrote diff(B,t), so it will differentiate it in terms of time, but it doesnt work, it results 0 , if I replace q with q(t) it returns an error because it thinks Im indexing.

How should I write this to calculate the derivative of B in terms of time ?

Answer 1

[Sulaymon Eshkabilov]

syms q(t) t a
diff(a*cos(q))

ans(t) = 

[Spulber Alexandru]

Thank you very much.

[Sulaymon Eshkabilov]

Most welcome! It is my pleasure! Merry Christmas!