# Question on form of differential

1. Sep 30, 2005

### Noone1982

My book says:

let p stand for partial, u is a function

p(uAx) / px = pu(Ax)/px + up(Ax)/px

How can it be valid?

2. Sep 30, 2005

### amcavoy

First of all, what is u a function of? Second, did you mean A(x)?

3. Sep 30, 2005

### Noone1982

u is just say xyz and Ax means A subscript x

4. Sep 30, 2005

### Integral

Staff Emeritus
It would help us all if you would take a few minutes to read through this thread . LaTex is really very easy and it makes it much easier to present problems such as yours.

5. Sep 30, 2005

### Noone1982

$$\frac{\partial }{\partial x}\left( uA_{x} \right)\; =\; \frac{\partial u}{\partial x}\left( A_{x} \right)+u\frac{\partial A_{x}}{\partial x}$$

To me, the right hand of the equation is saying the left hand twice rather than reworking it.

6. Sep 30, 2005

### Manchot

That's just the straight-up definition of the chain rule.

7. Oct 1, 2005

### Noone1982

Thanks! :)

Last edited: Oct 1, 2005