The Fundamental Theorem of Calculus proves that a function A(x) defined by a definite integral from a fixed point c to the value x of some function f(t), (A(x) = integral from c to x of f(t) dt) will be an antiderivative of f(x), or in other words A'(x) = f(x).

This short video illustrates how to use the chain rule in combination with the Fundamental Theorem of Calculus to compute derivatives of functions defined by integrals.