Hi,

I am having trouble understanding the following question:

There is a scalar field f(r) depending onr= (x,y,z) through r = $\displaystyle \sqrt[2]{x^2+y^2+z^2}$.

Show that $\displaystyle \nabla f = \frac{f'}{r}$rI know that grad f is normally each partial derivative i.e. (df/dx, df/dy, df/dz) but how do I calculate it when it only has r as the parameter?

I'm also unsure as to how you would calculate f' in this situation, as I can't see an equation to differentiate.

Anything that helps me understand this better is greatly appreciated.

Thanks.