General Leibniz rule
In calculus, the general Leibniz rule, named after Gottfried Wilhelm Leibniz, generalizes the product rule for the derivative of the product of two functions (which is also known as "Leibniz's rule"). It states that if f {\displaystyle f} and g {\displaystyle g} are n-times differentiable functions, then the product f g {\displaystyle fg} is also n-times differentiable and its n-th derivative is given by ( f g ) ( n ) = ∑ k = 0 n ( n k ) f ( n − k ) g ( k ) , {\displaystyle (fg)^{(n)}=\sum _{k=0}^{n}{n \choose k}f^{(n-k)}g^{(k)},} where ( n k ) = n !