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 f ∘ g (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:
The chain rule can also be written with a different notation for function composition (though still in Lagrange's notation for differentiation). The meaning is identical.
