Chain rule for differentiation

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This article is about a differentiation rule, i.e., a rule for differentiating a function expressed in terms of other functions whose derivatives are known.
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Statement for two functions

The chain rule is stated in many versions:

Version type Statement
specific point, named functions Suppose f and g are functions such that g is differentiable at a point x=x0, and f is differentiable at g(x0). Then the composite fg is differentiable at x0, and we have:
ddx[f(g(x))]|x=x0=f(g(x0))g(x0)
generic point, named functions, point notation Suppose f and g are functions of one variable. Then, we have
ddx[f(g(x))]=f(g(x))g(x) wherever the right side expression makes sense.
generic point, named functions, point-free notation Suppose f and g are functions of one variable. Then,
(fg)=(fg)g where the right side expression makes sense, where denotes the pointwise product of functions.
pure Leibniz notation Suppose u=g(x) is a function of x and v=f(u) is a function of u. Then,
dvdx=dvdududx

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