What is the (subtle) difference between the three ways to typeset unnumbered equations (if any)?
The first is the plain tex,
$$ E = mc^2 $$
The second is the LaTeX
\[ E = mc^2 \]
And the third is the AMS,
\begin{equation*}
E = mc^2
\end{equation*}
As far as I can tell, the end results are almost the same. If there's any difference, most likely in the spacing around the formulas. But I cannot find any concrete reference for the later two.
\usepackage{amsmath}, methods 2 and 3 are exactly the same. – egreg Jun 20 '16 at 09:50