What is the derivative of 5cos^2 (pi) (t) ? ... ?

The answer is

we know that (cosu (t)) ' = - u ' (t) sin u (t)

so (cos^2 (pi) (t)) ' = 2 (-pi sin pit) cospit

and finally the answer is

[5cos^2 (pi) (t) ] ' = - 10 pi sin pit cospit