Numbered Equation

How can I write numbers (enumerate) in front of the equation?? If I write with \item , be much space between enumerate numbers and equations.

• In the drawing the numbers appear to be above the equation, which is precisely how enumerate together with equation* works. Oct 23 '16 at 3:21
• Welcome to TeX.SX! You showed a prime bad example of bad typography! Not your fault, of course! Oct 24 '16 at 23:05

Use leqno class parameter:

\documentclass[leqno]{article}
\usepackage{amsmath}
\begin{document}
\begin{align}
y &= mx + b\\
y &= Ax^2 + Bx + c
\end{align}
\end{document}


Output below:

In the picture you show, the numbers are hanging from nowhere and the centering of the formulas has no meaning.

In the following, the formulas are on the same line as the numbers, separated from them by two quads.

\documentclass{article}
\usepackage{amsmath}
\usepackage{enumitem}

\usepackage{showframe}% just for the example

\begin{document}

\begin{enumerate}[itemsep=\baselineskip,itemindent=2em,labelsep=2em]

\item $\displaystyle \prod_{k=2}^{\infty}\left(1-\frac{2}{k(k+1)}\right)=\frac{1}{3}$

\item $\displaystyle \prod_{k=2}^{\infty}\left(1-\frac{2}{k^{3}+1)}\right)=\frac{2}{3}$

\item \begin{tabular}[t]{@{}c@{}}
$\displaystyle \prod_{k=1}^{\infty} \left(\frac{2k}{2k-1}\right) \left(\frac{2k}{2k+1}\right)= \frac{2}{1}\cdot\frac{2}{3}\cdot\frac{4}{3}\cdot \frac{4}{5}\cdot\frac{6}{5}\cdot\frac{6}{7}\dots=\frac{\pi}{2}$
\\
\bfseries (Wallis's formula)
\end{tabular}

\end{enumerate}

\end{document}


Just to mention how the original has been typeset:

\documentclass{article}
\usepackage{amsmath}

\usepackage{showframe} % just for the example

\begin{document}

\begin{enumerate}

\item $\prod_{k=2}^{\infty}\left(1-\frac{2}{k(k+1)}\right)=\frac{1}{3}$

\item $\prod_{k=2}^{\infty}\left(1-\frac{2}{k^{3}+1)}\right)=\frac{2}{3}$

\item \begin{gather*}
\prod_{k=1}^{\infty}
\left(\frac{2k}{2k-1}\right)
\left(\frac{2k}{2k+1}\right)=
\frac{2}{1}\cdot\frac{2}{3}\cdot\frac{4}{3}\cdot
\frac{4}{5}\cdot\frac{6}{5}\cdot\frac{6}{7}\dots=\frac{\pi}{2}
\\
\textbf{(Wallis's formula)}
\end{gather*}

\end{enumerate}
\end{document}


Example which centers the equations and puts the numbers to the left.

\documentclass{article}

\newcounter{eqitem}
\newcommand*{\eqitem}[1]{%
\refstepcounter{eqitem}%
$\hbox to \displaywidth{\displaystyle \rlap{\theeqitem.}% \hfil#1\hfil }%$%
}
\begin{document}
\setcounter{eqitem}{0}
\eqitem{\prod_{k=2}^\infty \left(1 - \frac{2}{k(k+1)}\right) = \frac{1}{3}}
\eqitem{\prod_{k=2}^\infty \left(1 - \frac{2}{k^3 + 1}\right) = \frac{2}{3}}
\eqitem{\prod_{k=2}^\infty \left(1 + \frac{1}{2^k - 2}\right) = 2}
\end{document}


Also, an environment can be defined:

\documentclass{article}

\newcounter{eqitem}
\newcommand*{\eqitem}[1]{%
\refstepcounter{eqitem}%
$\hbox to \displaywidth{\displaystyle \rlap{\theeqitem.}% \hfil#1\hfil }%$%
}
\newenvironment*{eqitemize}{%
\setcounter{eqitem}{0}%
\let\item\eqitem
}{}

\begin{document}
\begin{eqitemize}
\item{\prod_{k=2}^\infty \left(1 - \frac{2}{k(k+1)}\right) = \frac{1}{3}}
\item{\prod_{k=2}^\infty \left(1 - \frac{2}{k^3 + 1}\right) = \frac{2}{3}}
\item{\prod_{k=2}^\infty \left(1 + \frac{1}{2^k - 2}\right) = 2}
\end{eqitemize}
\end{document}

• Why not defining an environment instead? Oct 25 '16 at 3:24
• @user94293 Answer updated to show, how it can be wrapped in an environment. Oct 25 '16 at 4:10