# Math Help - [SOLVED] vector identity proof

1. ## [SOLVED] vector identity proof

Need help proving this
let f(x,y,z) and g(x,y,z) be any C^2 scaler functions. Without using the basic identities of vector analysis prove that

thanks

2. Originally Posted by sam1986
Need help proving this
let f(x,y,z) and g(x,y,z) be any C^2 scaler functions. Without using the basic identities of vector analysis prove that

thanks
To start you off:

$\nabla.(f \nabla g-g \nabla f)=\sum_i \frac{\partial}{\partial x_i}$ $
(f \nabla g-g \nabla f)_i$
$
=\sum_i \frac{\partial}{\partial x_i} \left( f\frac{\partial g}{\partial x_i}-g\frac{\partial f}{\partial x_i}\right)
$

Now apply the product rule to the what is inside the right most summation
and simplify and you should have what you want.

RonL