Find f(r) such that \(\nabla f = \frac{{\vec r}}{{{r^5}}}\) and f(1) = 0
1
\(\frac{1}{3}\left( {1 - \frac{1}{{{r^4}}}} \right)\)
2
\(\frac{1}{3}\left( {1 + \frac{1}{{{r^3}}}} \right)\)
3
\(\frac{1}{3}\left( {1 + \frac{1}{{{r^4}}}} \right)\)
4
\(\frac{1}{3}\left( {1 - \frac{1}{{{r^3}}}} \right)\)