Difference between revisions of "2011 IMO Problems"
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Revision as of 17:19, 20 July 2011
Let f : R → R be a real-valued function defined on the set of real numbers that satisfies f(x + y) ≤ yf(x) + f(f(x)) for all real numbers x and y. Prove that f(x) = 0 for all x≤ 0.