[tex]v = \frac{eEt/m_o}{\sqrt{1 + (eEt)^2/(m_oc)^2}}[/tex]

Clearly the asymptote is c (speed of light) and I think I'm being asked to find an expression like constant * (1 + a1 / t + a2 / t^2 + ...) but I have not been able to do so. Power series don't work and binomial thm doesn't apply. Please help.