Paper 2, Section I, F

Topics in Analysis | Part II, 2017

Are the following statements true or false? Give reasons, quoting any theorems that you need.

(i) There is a sequence of polynomials PnP_{n} with Pn(t)→sin⁡tP_{n}(t) \rightarrow \sin t uniformly on R\mathbb{R} as n→∞n \rightarrow \infty.

(ii) If f:R→Rf: \mathbb{R} \rightarrow \mathbb{R} is continuous, then there is a sequence of polynomials QnQ_{n} with Qn(t)→f(t)Q_{n}(t) \rightarrow f(t) for each t∈Rt \in \mathbb{R} as n→∞n \rightarrow \infty.

(iii) If g:[1,∞)→Rg:[1, \infty) \rightarrow \mathbb{R} is continuous with g(t)→0g(t) \rightarrow 0 as t→∞t \rightarrow \infty, then there is a sequence of polynomials RnR_{n} with Rn(1/t)→g(t)R_{n}(1 / t) \rightarrow g(t) uniformly on [1,∞)[1, \infty) as n→∞n \rightarrow \infty.

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