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MathNet 2020 — Math Olympiad Vault — Part 06 Question 107

Math Olympiad Vault · MathNet 2020 — Math Olympiad Vault — Part 06

Question 107

A sequence $(x_n)$ is defined as follows $x_1 = 1$ and $x_{n+1} = x_n + 3\sqrt{x_n} + \frac{n}{\sqrt{x_n}}$ for all positive integers $n$.

a) Prove that $\lim_{n \to +\infty} \frac{n}{x_n} = 0$.

b) Find the limit $\lim_{n \to +\infty} \frac{n^2}{x_n}$.