Can someone help me with how to do the following:

A thin column of radius a and charge density \rho_c surronds the z axis

\rho_c(R) = \{\begin{array}{cc}\rho_{0},&<br />
R\leq a\\0, &  R>a\end{array}


(a) In cylindrical coordinates the electric field is \underline{E} = E_R(R)\underline{{e_R}}. Apply the divergence theorem to a cylinder of radius R > a amd of UNIT length in z to demonstrate that

{E_R}(R) = \frac{\rho_0a^2}{2\epsilon_0R}
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I know that \nabla \cdot E = \frac{\rho_c}{\epsilon}

and I know the divergence theorem but I can't figure out how to do this

- Jason