Paper 3, Section I, F

Topics in Analysis | Part II, 2011

Let Γ={z∈C:z≠1,∣Re⁡(z)∣+∣Im⁡(z)∣=1}\Gamma=\{z \in \mathbb{C}: z \neq 1,|\operatorname{Re}(z)|+|\operatorname{Im}(z)|=1\}.

(i) Prove that, for any ζ∈C\zeta \in \mathbb{C} with ∣Re⁡(ζ)∣+∣Im⁡(ζ)∣>1|\operatorname{Re}(\zeta)|+|\operatorname{Im}(\zeta)|>1 and any ϵ>0\epsilon>0, there exists a complex polynomial pp such that

sup⁡z∈Γ∣p(z)−(z−ζ)−1∣<ϵ\sup _{z \in \Gamma}\left|p(z)-(z-\zeta)^{-1}\right|<\epsilon

(ii) Does there exist a sequence of polynomials pnp_{n} such that pn(z)→(z−1)−1p_{n}(z) \rightarrow(z-1)^{-1} for every z∈Γ?z \in \Gamma ? Justify your answer.

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