Math Help - derivative of an integral

1. derivative of an integral

Consider the following:

derivative of the integral of cos(t)*dt

^lower limit of integral = 0
^upper limit of integral - 3x

when evalutating this, would the answer be 3cos(3x)

??

Fundamental theorem of calculus - Wikipedia, the free encyclopedia

and Leibniz integral rule:

Leibniz integral rule - Wikipedia, the free encyclopedia