Hi Fabrice,

I think you have to use
         \startalign[n=3,align={left,right}]
and finish the alignment with
        \stopalign

Is this what you are looking for?

\starttext
\startformula
  \startalign[n=3,align={left,right}]
   \NC \qquad \NC\frac{\lvert\overline{AD}\rvert}{\lvert\overline{CD}\rvert} \NC =\frac{\lvert\overline{DC}\rvert}{\lvert\overline{CE'}\rvert}\NR
   \NC \iff \NC  \frac{1}{x}  \NC =\frac{x}{1-x} \NR
   \NC \iff \NC 1-x \NC =x^2 \NR
   \NC \iff \NC 0\NC =x^2+x-1 \NR
  \stopalign
\stopformula
\stoptext

Best regards: OK

> On 5 Jan 2019, at 12:27, Fabrice Couvreur <fabrice1.couvreur@gmail.com> wrote:
>
> Hi,
> I'm trying to get the same result for this file compiled with latex.
> Thanks.
> Fabrice
>
> \documentclass{article}
> \usepackage{amsmath}
>
>
>
> \begin{document}
>
>
>
> \begin{alignat*}{2}
> &\qquad&
>
>   
> \frac{\lvert\overline{AD}\rvert}{\lvert\overline{CD}\rvert}
>
>     
> &=\frac{\lvert\overline{DC}\rvert}{\lvert\overline{CE'}\rvert}\\
> \iff&& \frac{1}{x}&=\frac{x}{1-x}\\
> \iff&& 1-x&=x^2\\
> \iff&& 0&=
> x^2+x-1
>
> \end{alignat*}
>
>
>
> \end{document}
>
> \starttext
> \startformula
>   \startmathalignment[n=3]
>    \NC \qquad \NC\frac{\lvert\overline{AD}\rvert}{\lvert\overline{CD}\rvert} \NC =\frac{\lvert\overline{DC}\rvert}{\lvert\overline{CE'}\rvert}\NR
>    \NC \iff \NC  \frac{1}{x}  \NC =\frac{x}{1-x} \NR
>    \NC \iff \NC 1-x \NC =x² \NR
>    \NC \iff \NC 0\NC =x²+x-1 \NR
>   \stopmathalignment
> \stopformula
> \stoptext
>
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>
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___________________________________________________________________________________
If your question is of interest to others as well, please add an entry to the Wiki!

maillist : ntg-context@ntg.nl / http://www.ntg.nl/mailman/listinfo/ntg-context
webpage  : http://www.pragma-ade.nl / http://context.aanhet.net
archive  : https://bitbucket.org/phg/context-mirror/commits/
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