Question

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

Answer 1

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