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MathNet 2025 — Part 02 (100 complete bilingual questions) Question 76

Math Olympiad Vault · MathNet 2025 — Part 02 (100 complete bilingual questions)

Question 76

Let $f : [0, \infty) \to [0, \infty)$ be a continuous bijective function, such that
$$
\lim_{x \to \infty} \frac{f^{-1}(f(x)/x)}{x} = 1.
$$

a) Show that $\lim_{x \to \infty} \frac{f(x)}{x} = \infty$ and $\lim_{x \to \infty} \frac{f^{-1}(ax)}{f^{-1}(x)} = 1$, for any $a \gt 0$.

b) Give an example of a function $f$ that satisfies the conditions from the statement.