Paper 2, Section I, F

Topics in Analysis | Part II, 2013

(i) Show that for every ϵ>0\epsilon>0 there is a polynomial p:R→Rp: \mathbb{R} \rightarrow \mathbb{R} such that ∣1x−p(x)∣⩽ϵ\left|\frac{1}{x}-p(x)\right| \leqslant \epsilon for all x∈Rx \in \mathbb{R} satisfying 12⩽∣x∣⩽2\frac{1}{2} \leqslant|x| \leqslant 2.

[You may assume standard results provided they are stated clearly.]

(ii) Show that there is no polynomial p:C→Cp: \mathbb{C} \rightarrow \mathbb{C} such that ∣1z−p(z)∣<1\left|\frac{1}{z}-p(z)\right|<1 for all z∈Cz \in \mathbb{C} satisfying 12⩽∣z∣⩽2\frac{1}{2} \leqslant|z| \leqslant 2.

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