<P> 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: </P> <Dl> <Dd> (f ∘ g) ′ = (f ′ ∘ g) ⋅ g ′ . (\ displaystyle (f \ circ g)' = (f' \ circ g) \ cdot g' .) </Dd> </Dl> <Dd> (f ∘ g) ′ = (f ′ ∘ g) ⋅ g ′ . (\ displaystyle (f \ circ g)' = (f' \ circ g) \ cdot g' .) </Dd> <P> This may equivalently be expressed in terms of the variable . Let F = f ∘ g, or equivalently, F (x) = f (g (x)) for all x . Then one can also write </P>

When is the chain rule used in differentiation