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Putnam 1962 A4

Source: Putnam 1962

May 15, 2022
PutnamDerivativesinequalities

Problem Statement

Assume that f(x)1|f(x)|\leq 1 and f(x)1|f''(x)|\leq 1 for all xx on an interval of length at least 2.2. Show that f(x)2|f'(x)|\leq 2 on the interval.