# Product rule

In calculus, the **product rule** (or **Leibniz rule**[1] or **Leibniz product rule**) is a formula used to find the derivatives of products of two or more functions. For two functions, it may be stated in Lagrange's notation as

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or in Leibniz's notation as

The rule may be extended or generalized to products of three or more functions, to a rule for higher-order derivatives of a product, and to other contexts.