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My friend came across this strange equation and I cant find mathematical way to find $x$ without drawing $x$ and $-\ln(x)$ and see that they come across at almost $x=0.5$.

Can any one help?

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  • $\begingroup$ I'm pretty sure there isn't an algebraic answer. I think the best you can do is approximate it numerically. I could be wrong, though. $\endgroup$ – Zach Stone Apr 3 '16 at 20:02
  • $\begingroup$ Can you give an answer? $\endgroup$ – Stav Alfi Apr 3 '16 at 20:03
  • $\begingroup$ We literally get these sort of questions everyday! $\endgroup$ – MathematicsStudent1122 Apr 3 '16 at 20:19
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$$x+\ln x=0$$ $$e^{x+\ln x}=e^0=1$$ $$xe^x=1$$

This can be solved by lambert $W$:

$$x=W(1)$$

There is a special name to this constant, it is called the omega constant.

You can find the numerical approximation via Newtons method.

Let $x_1=0.5$

And

$$x_{n+1}=x_{n}-\frac{x_n+\ln x_n}{1+\frac{1}{x_n}}$$

As

$$n \to \infty$$

Then you get closer to the approximate value:

$$x=.56714329...$$

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