(i) Let −1<α<0 and let
f(z)=zlog(z−α) where −π⩽arg(z−α)<πg(z)=zlogz where −π⩽arg(z)<π
Here the logarithms take their principal values. Give a sketch to indicate the positions of the branch cuts implied by the definitions of f(z) and g(z).
(ii) Let h(z)=f(z)−g(z). Explain why h(z) is analytic in the annulus 1⩽∣z∣⩽R for any R>1. Obtain the first three terms of the Laurent expansion for h(z) around z=0 in this annulus and hence evaluate
∮∣z∣=2h(z)dz