Chain Rule

In calculus, the chain rule is a formula that expresses the derivative of the composition of two differentiable functions f and g in terms of the derivatives of f and g. More precisely, if h = f ∘ g {\displaystyle h=f\circ g} is the function such that h ( x ) = f ( g ( x ) ) {\displaystyle h(x)=f(g(x))} for every x, then the chain rule is, in Lagrange's notation,