# Derivative notation

1. Sep 22, 2011

### intervoxel

What is the meaning of

$\frac{\partial F(x)}{\partial(\partial f(x)/\partial x)}$

in which a derivative appears in place of the variable x in the denominator?

2. Sep 23, 2011

### mathman

Let u = ∂f(x)/∂x. Then the expression is ∂F(x)/∂u. In order to make sense out of it you need to know F(x) and f(x).

3. Sep 24, 2011

Thank you.