In calculus, the product rule (or Leibniz rule 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

(
f

g

)

=

f

g
+
f

g

{\displaystyle (f\cdot g)'=f'\cdot g+f\cdot g'}
or in Leibniz's notation as

d

d
x

(
u

v
)
=

d
u

d
x

v
+
u

d
v

d
x

.

{\displaystyle {\dfrac {d}{dx}}(u\cdot v)={\dfrac {du}{dx}}\cdot v+u\cdot {\dfrac {dv}{dx}}.}
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.

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