DefinitionThe chain rule is a very important theorem in calculus that shows how to differentiate composite functions. That if a function f is the composition of two functions g and h, the derivative of f with respect to the independent variable is the derivative of g with respect to its variable times the derivative of h with respect to its variable. The chain rule is a major ingredient in calculus for dealing with derivatives of functions given implicitly or in terms of their components. For instance: The Chain Rule in physics to find the velocity of an object moving in a circular path, where the postion function is a composition of trig functions.