对齐乳胶方程

Question

I am a beginner in latex.I have the following piece of latex code. The code is working fine but I want that all the equality operators of each equation should be aligned. How can it be done?

\begin{enumerate}
\item[Commutative] $a+b = b+a$
\item[Associative] $a+(b+c)=(a+b)+c$
\item[Distributive] $a(b+c)=ab+ac$
\end{enumerate}

Answer 1

I'm unsure if this is possible inside the enumerate environment. An easy alternative is to use a tabular environment instead. In the example below the left and right sides of the equation are contained in two separate columns, with an = appearing between them.

\documentclass[12pt]{article}

\begin{document}
\begin{tabular}{l r@{$=$}l}
    Commutative & $a+b$ & $b+a$ \\
    Associative & $a+(b+c)$ & $(a+b)+c$ \\
    Distributive & $a(b+c)$ & $ab+ac$ \\
\end{tabular}
\end{document}

Answer 2

Using \\eqmakebox[<tag>][<align>] (from eqparbox ) you can have all elements under the same <tag> be placed in a box of maximum width, together with individual <align> ment as needed. Below I has \\eqmakebox[LHS][r] to ensure all elements tagged LHS is r ight-aligned. The result is alignment around the = .

\documentclass{article}

\usepackage{eqparbox}

\begin{document}

\begin{enumerate}
  \item[Commutative]  $      a + b = b + a      $
  \item[Associative]  $a + (b + c) = (a + b) + c$
  \item[Distributive] $   a(b + c) = ab + ac    $
\end{enumerate}

\begin{enumerate}
  \item[Commutative]  $      \eqmakebox[LHS][r]{$a + b$} = b + a      $
  \item[Associative]  $\eqmakebox[LHS][r]{$a + (b + c)$} = (a + b) + c$
  \item[Distributive] $   \eqmakebox[LHS][r]{$a(b + c)$} = ab + ac    $
\end{enumerate}

\end{document}

Alternatively you can measure the widest element yourself:

\newlength{\widestelement}
\settowidth{\widestelement}{$a + (b + c)$}

and then use

\begin{enumerate}
  \item[Commutative]  $      \makebox[\widestelement][r]{$a + b$} = b + a      $
  \item[Associative]  $\makebox[\widestelement][r]{$a + (b + c)$} = (a + b) + c$
  \item[Distributive] $   \makebox[\widestelement][r]{$a(b + c)$} = ab + ac    $
\end{enumerate}