Interesting Limit

**Media_Man** · June 10th 2009, 09:32 AM

Evaluate: $<br /> <br /> \lim_{x\rightarrow 0}\left(\frac{(1 + x)^{\frac{1}{x}}}{e}\right)^{\frac{1}{x}}<br />$

**fardeen_gen** · June 10th 2009, 09:49 AM

One of the first I had encountered when I started limits.

Answer:

Spoiler:

I leave it to the other members to see if they know how to do it.
HINT:

Spoiler:

**Random Variable** · June 10th 2009, 10:44 AM

My attempt:

first find $\lim_{x \to 0} \ \ln \Bigg( \Big( \frac {(1+x)^{1 \over x}}{e} \Big)^{1 \over x} \Bigg)$

$= \lim_{x \to 0} \ \frac {1}{x} \Big( \ln (1+x)^{1 \over x} - \ln(e) \Big)$

$= \lim_{x \to 0} \ \frac {1}{x} \Big( \frac {1}{x} \ln (1+x) - 1 \Big)$

$= \lim_{x \to 0} \frac {\ln(1+x)-x}{x^{2}}$

which is the indeterminate form $0 \over 0$

applying L'Hospital's rule

$= \lim_{x \to 0} \frac {\frac{1}{1+x}-1}{2x}$

applying L'Hospital's rule a second time

$= \lim_{x \to 0} \frac {\frac{-1}{(1+x)^{2}}}{2} = -\frac {1}{2}$

so the limit of the original function is $e^{-\frac{1}{2}}$

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