Originally Posted by

**limddavid** Not sure if the description fits the question I have, but here it goes:

"If a vector function **f**(x,y,z) is not irrotational but the product of f and a scalar function g(x,y,z) is irrotational, show that then:

$\displaystyle \mathbf{f}\cdot \boldsymbol{\triangledown} \times \mathbf{f}=0$"

I've been working at this for a couple hours now... I was able to find that since:

$\displaystyle \boldsymbol{\triangledown} \times (g\mathbf{f})=0$

and

$\displaystyle \boldsymbol{\triangledown} \times (g\mathbf{f})=g(\triangledown \times \mathbf{f})+(\triangledown g)\times \mathbf{f}$,

then

$\displaystyle g(\triangledown \times \mathbf{f})=-(\triangledown g)\times \mathbf{f}$

I don't even know if this is in the right direction. Help!