Convergence of Exponential Function of Sequence

Question

If $x_n$ is a sequence such that $x_n \neq 0$, and $x_n \rightarrow 0$, then prove:

$$\lim_{n \rightarrow \infty} \frac{\exp(x_n) - 1}{x_n} = 1.$$

where $\exp()$ is the exponential function. I was wondering if I would be able to use the fact that if $x_n \rightarrow 0$, then $\exp(x_n) \rightarrow 1$ in this proof, but I'm skeptical of using that because the numerator would approach $0.$ I just need a bit of guidance/maybe a hint. Thanks in advance!

Answer 1

Observe that : $$ \left(\forall x\in\left[-1,1\right]\right),\ \left|\mathrm{e}^{x}-1\right|=\left|x\right|\int_{0}^{1}{\mathrm{e}^{xt}\,\mathrm{d}t}\leq \left|x\right|\int_{0}^{1}{\mathrm{e}^{t}\,\mathrm{d}t}=\left|x\right|\left(\mathrm{e}-1\right) $$

If $ \left(x_{n}\right)\in\mathbb{R}^{\mathbb{N}} $ such that $ x_{n}\underset{n\to +\infty}{\longrightarrow}0 $, then $ \left(\exists n_{0}\in\mathbb{N}\right)\left(\forall n\geq n_{0}\right),\ \left|x_{n}\right|\leq 1 $

Using the same trick : $$ \left(\forall n\geq n_{0}\right),\ \left|\frac{\mathrm{e}^{x_{n}}-1}{x_{n}}-1\right|=\left|\int_{0}^{1}{\left(\mathrm{e}^{x_{n}t}-1\right)\mathrm{d}t}\right|\leq\int_{0}^{1}{\left|\mathrm{e}^{x_{n}t}-1\right|\mathrm{d}t}\leq\left|x_{n}\right|\frac{\mathrm{e}-1}{2}\underset{n\to +\infty}{\longrightarrow}0 $$

Thus $$ \lim_{n\to +\infty}{\frac{\mathrm{e}^{x_{n}}-1}{x_{n}}}=1 $$

Answer 2

It is a direct consequence of the basic limit $$\lim_{t\to 0}\frac{e^t-1}{t}=1 $$ together with the sequential definition of a limit of a function which applied to the limit above gives you the precise statement that has to be shown.