chain rule

In calculus, the chain rule is a formula for computing the derivative of the composition of two or more functions. That is, if f and g are functions, then the chain rule expresses the derivative of their composition (the function which maps x to f(g(x)) in terms of the derivatives of f and g and the product of functions as follows:

This can be written more explicitly in terms of the variable. Let , or equivalently, for all x. Then one can also write