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