Walker, Halliday & Resnick — Electric Fields: Problem 2

2 The electric field of an electric dipole along the dipole axis is approximated by Eqs. 22-8 and 22-9. If a binomial expansion is made of Eq. 22-7, what is the next term in the expression for the dipole’s electric field along the dipole axis? That is, what is $E_{next}$ in the expression $E = \frac{1}{2\pi\epsilon_0}\frac{qd}{z^3} + E_{next}$?