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?

  • 1
    $\begingroup$ 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, 2016 at 20:02
  • $\begingroup$ Can you give an answer? $\endgroup$
    – Stav Alfi
    Apr 3, 2016 at 20:03
  • 1
    $\begingroup$ We literally get these sort of questions everyday! $\endgroup$ Apr 3, 2016 at 20:19

1 Answer 1


$$x+\ln x=0$$ $$e^{x+\ln x}=e^0=1$$ $$xe^x=1$$

This can be solved by lambert $W$:


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

You can find the numerical approximation via Newtons method.

Let $x_1=0.5$


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


$$n \to \infty$$

Then you get closer to the approximate value:



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