Hello, everyone!
I'm stuck at the following problem.
Let us have an equation that I intend to solve with some numerical method:
$\displaystyle |x (e^{1/x} - 1) - 1| = \epsilon$, where $\displaystyle \epsilon$ is a small number and $\displaystyle x$ is positive.
First off, I want to get rid of the modulus sign to avoid solving a system of equations. To do so, I need to show that
$\displaystyle \forall x > 0: x (e^{1/x} - 1) > 1$
(This fact I established empirically and want to prove. The plot can be seen
here: 1 is actually a limit).
The inequality is equivalent to the following one:
$\displaystyle e^{1/x} > \frac{1}{x} + 1$
$\displaystyle {\frac{1}{x}} > \ln{\left(\frac{1}{x} + 1\right)}$
Denote $\displaystyle 1 + \frac{1}{x} = u$ ($\displaystyle u > 1$), then
$\displaystyle u > 1 + \ln{u}$
And here's where I'm out of ideas. How do I analytically prove the last inequality for all $\displaystyle u > 1$?
Any thoughts would be very appreciated!
PS I probably should have posted this in Calculus subforum, my bad.