How do I number equations with roman numbers?

Question

I would like to display a set of equations with roman numerals on the left side. The equations should be left aligned and the = should be aligned. Something like that:

I)   ae + bg = ae + cf \Leftrightarrow bg = cf
II)  af + bh = be + df
III) ce + dg = ag + ch
IV)  cf + dh = bg + dh \Leftrightarrow cf = bg

How do I generally write left-aligned equations with roman numerals? How do I make it with mathjax?

This is the best I came up with:

\begin{eqnarray*}
  I)   & ae + bg &= ae + cf &\Leftrightarrow bg = cf \\
  II)  & af + bh &= be + df\\
  III) & ce + dg &= ag + ch\\
  IV)  & cf + dh &= bg + dh &\Leftrightarrow cf = bg
\end{eqnarray*}

With this solution, the numeration is italic.

Answer 1

\documentclass[leqno]{article}
\usepackage{amsmath}
\usepackage{enumitem}
\renewcommand{\theequation}{\roman{equation}}
\newcommand{\pp}[1]{\phantom{#1}}
\begin{document}
\section{Lipsum lupsum}
\begin{align}
ae + bg & = ae + cf \Leftrightarrow bg = cf \\
af + bh & = be + df \\
ce + dg & = ag + ch \\
cf + dh & = bg + dh \Leftrightarrow cf = bg
\end{align}

\begin{enumerate}[label=(\roman{*}),labelsep=2em]
\item  $ae + bg  =  ae + cf \Leftrightarrow bg = cf$ 
\item  $af + bh  =  be + df$ 
\item  $ce + dg  =  ag + ch$ 
\item  $cf + dh  =  bg + dh \Leftrightarrow cf = bg$
\end{enumerate}

\end{document}

Another way is to use \tag{i} .. and so forth on every line, but this is somewhat cumbersome. Alternatively look here

http://www.mathjax.org/docs/2.0/options/TeX.html#configure-tex

Include something like

MathJax.Hub.Config({
  TeX: {
    Macros: {
      TagSide: "left",
      equationNumbers: {formatNumber: function (n) {return \Roman{*}}}
    }
  }
});

in a tex section in your MathJax.Hub.Config() call.