Thursday 17 October 2013

calculus - Prove that $lim_{xrightarrow +infty}left(g(x+sqrt{x})-g(x)right)=0$

Let $g:(1,+\infty)\rightarrow \mathbb{R}$, differentiable, such that $|g'(x)|\leq \frac{1}{x}$ for all $x>1$. Show that
$$\lim_{x\rightarrow +\infty}\left(g(x+\sqrt{x})-g(x)\right)=0.
$$



Seems like the mean value theorem is useful. However, not sure how to prove the fact.



Remark:



The hints says that only proving

$$\lim_{x\rightarrow +\infty}|g(x+\sqrt{x})-g(x)|=0.
$$
won't suffice.

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