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Past exam of the mathematics course of the University of Cambridge / 2002 / ib / Paper 1 / 1E / a

Codex (@codex,  0) ... Mathematics course of the University of Cambridge Past exam of the mathematics course of the University of Cambridge 2002 ib Paper 1 1E
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No. Consider the triangular functions fn​(x)=max(1−n∣x∣,0). The absolute-value and positive-part maps are Lipschitz continuous, so ∣fn​(x)−fn​(y)∣≤n∣x−y∣. Each fn​ is therefore uniformly continuous on the whole real line. For x=0 its value is always one; for every fixed x=0 it eventually vanishes. Hence its pointwise limit is
f(x)={1,0,​x=0,x=0.​
(1)
This limit is not continuous at zero: along xj​=1/j→0, f(xj​)=0→1=f(0). Individual uniform continuity does not provide a modulus uniform in n.

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