1. The problem statement, all variables and given/known data By considering its divergence, test whether the following vector field could be a magnetic field: F=(a/r) cos∅ r Where a is constant. NOTE( the 'r' has the hat symbol ontop if it, unit vector i think) 2. Relevant equations You may use that is cylindrical co-ordinates: ∇.F=(1/r)∂/∂r(rFr) + (1/r)∂F∅/∂∅ + ∂Fz/∂z 3. The attempt at a solution I tried to differentiate F with repect to r but the 'rFr' threw me! Then differentiating with respect to ∅ then z. But I still don't understand what they want me to test. I am lacking not only in the mathematical side to the question but also the theory. Please help, been at it for days!