1. The problem statement, all variables and given/known data Show that, if a charge distribution has cylindrical symmetry, then knowing the value of Qzz allows you to determine the entire quadrupole moment matrix. 2. Relevant equations Tr Q=0, ie Qxx+Qyy+Qzz=0 3. The attempt at a solution Because of the cylindrical symmetry, the charge density changes as a function of ρ, where ρ=(x^2+y^2)^1/2. Then I don't really know where to go from there.