MHB How to Evaluate a Limit Involving Infinity using L'Hopital's Rule

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To evaluate the limit $$\lim_{x->\pm\infty}xe^{\frac{2}{x}}-x$$ using L'Hopital's Rule, the initial approach involves dividing by x, leading to an incorrect conclusion of 0. The correct method is to rewrite the limit as $$\dfrac{e^{2/x}-1}{1/x}$$, which simplifies the evaluation. After applying L'Hopital's Rule, the limit resolves to 2. The final expression confirms that the limit approaches 2 as x approaches infinity.
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Hello MHB,
$$\lim_{x->\pm\infty}xe^{\frac{2}{x}}-x$$
I start to divide by x and we know that $$\lim_{x->\pm\infty} \frac{2}{x}=0$$
with other words we get $$1-1=0$$ but that is wrong, how do I do this :confused:

Regards,
$$|\pi\rangle$$
 
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Re: limit

Rewrite: $$\dfrac{e^{2/x}-1}{1/x}$$
 
Re: limit

tkhunny said:
Rewrite: $$\dfrac{e^{2/x}-1}{1/x}$$
Thanks solved it now!:) got 2 as answer now!:)

Regards,
$$|\pi\rangle$$
 
Re: limit

$$x(e^{\frac{2}{x}}-1) = x ( 1+\frac{2}{x}+\frac{2}{x^2}+\mathcal{o}(\frac{1}{x^2})-1 )$$

$$x( \frac{2}{x}+\frac{2}{x^2}+\mathcal{o} (\frac{1}{x^2}) ) = 2+\frac{2}{x}+\mathcal{o} (\frac{1}{x}) $$
 
There are probably loads of proofs of this online, but I do not want to cheat. Here is my attempt: Convexity says that $$f(\lambda a + (1-\lambda)b) \leq \lambda f(a) + (1-\lambda) f(b)$$ $$f(b + \lambda(a-b)) \leq f(b) + \lambda (f(a) - f(b))$$ We know from the intermediate value theorem that there exists a ##c \in (b,a)## such that $$\frac{f(a) - f(b)}{a-b} = f'(c).$$ Hence $$f(b + \lambda(a-b)) \leq f(b) + \lambda (a - b) f'(c))$$ $$\frac{f(b + \lambda(a-b)) - f(b)}{\lambda(a-b)}...

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