I Need help with a derivative solution

1. Aug 28, 2016

Dyatlov

Hello.
We have the derivative of a function: d F(x)/dx. If we substitute x = au, how can I show that d F(x)/dx = (1/a) (dF/du) ?

2. Aug 28, 2016

QuantumQuest

When you do a substitution, you take the derivatives of both sides (hint: take into account what is constant and what is not). If you do this, you'll immediately come to what you need to show.

3. Aug 28, 2016

Dyatlov

Thanks for the answer, did it and got:
(dF/da) (dF/du) = (dF/da) u + (dF/du) a = (dF/du) a, since a is a constant. What am I missing here?

4. Aug 28, 2016

QuantumQuest

As I previously said, note that $dx = a\cdot du$.

5. Aug 28, 2016

Dyatlov

Thanks, got it now.