# Simple help with notation

1. Aug 29, 2007

### duckywitbigfeet

ok i am pretty good with the topic but i need help with this notation i actually have never seen it before i was wondering if anyone could put in a way that i might have seen it..

the problem is uxx+uyy = 0

2. Aug 29, 2007

### d_leet

$$u_{xx}=\frac{\partial^{2}u}{\partial x^{2}}$$

And similarly for uyy, just replace x with y.

Last edited: Aug 29, 2007
3. Aug 30, 2007

### Nesk

If I remember correctly, the general form of that notation is:
$$u_{x_1 , ..,x_n} \equiv \frac{\partial ^n u}{\partial x_n... \partial x_1}$$