Newtonian geodesic deviation

Please show that the relative distance $\delta_i$ between two objects in Newtonian gravity is given by \(\frac{\mathrm{d}^2\delta_i}{\mathrm{d}t^2} = \sum_j\partial^2_{ij}\Phi\:\delta_j\) for small \(\delta_i\). What would be different in the true, relativistic geodesic deviation?