I'm reading Control Systems Engineering of Nise, Appendice M.1, Derivation of the Behaviour of the Root Locus at Infinity (Kuo, 1987).
At one point, we have;
$$ f(s) = (1+\frac{b1-a1}{s})^{1/n} $$
is expanded into infinite series and the first two terms are significant. We obtain; $$ (1+\frac{b1-a1}{ns}) $$
I tried expanding into Taylor Series but couldn't derive the same expression. Missing something?