# Homework Help: Can anyone check this identity please?

1. Sep 7, 2011

### Deathcrush

1. The problem statement, all variables and given/known data

I just want to check if this identity is true, since I have not found it anywhere, can anyone help me?

v is a vector (and that nu is supposed to be a v too)

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2. Sep 7, 2011

### LCKurtz

The "identity" only makes sense if one of the factors is a scalar, and it's wrong even then. I think you want this, where f is a scalar function and V is a vector function:

$$\nabla \cdot f\vec V = \nabla f \cdot \vec V + f (\nabla \cdot \vec V)$$

3. Sep 7, 2011

### Deathcrush

I finally found it, looks like I was missing another term in the right side v(Div(v)), altough this is 0 in my case because im working with fluid dynamics. Now everything makes perfect sense, thanks anyway