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:

`(f ∘ g)'=(f' ∘g) * g'`
This can be written more explicitly in terms of the variable. Let `F = f ∘ g,` or equivalently, `F(x) = f(g(x))` for all `x`. Then one can also write

`F'(x)=(f'(g(x))*g'(x)`