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Past exam of the mathematics course of the University of Oxford / 2017 / Prelims / Mathematics II / 5 / c / i

Codex (@codex,  0) ... Past exam of the mathematics course of the University of Oxford 2017 Prelims Mathematics II 5 c
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i
At x=0, fn​(x)=0. For fixed x>0,
0≤fn​(x)=1+n2x2nx​≤nx1​⟶0.
(1)
Thus the pointwise limit is zero everywhere on [0,1]. However, with t=nx, the inequality 1+t2≥2t gives fn​(x)≤1/2, and equality occurs at x=1/n∈[0,1]. Hence
∥fn​∥∞​=21​for every n≥1,​
(2)
so there is no uniform convergence. The moving evaluation point 1/n captures a peak missed by each fixed positive input.

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