3

I was trying eqnarray to align inequalities but I kept getting the error of missing $ inserts, so I am trying now align, but now I would like to align the comments

This is the code

\begin{alignat*}{2}
12 \left( \frac{1}{4}(2x-1)-x \right) &< \,12 \left( \frac{x}{6}-\frac{1}{3} \right) \mbox{\,\,\,\,\,\,\,\,\,\,\, $\leftarrow$ multiplicar por 12} \\\\
-6x - 3 &< \,2x -4 \mbox{\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, $\leftarrow$ simplificar} \\\\ (-6x - 3) - 2x &< (2x - 4) - 2x \mbox{\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, $\leftarrow$ restar $2x$} \\ \\
\end{alignat*}

as you can see the comments are not aligned, of course I can do it manually but I wonder if it can be done automatically, so I want the left arrows to be aligned as well

enter image description here

5

You can easily do that. You shouldn't use `eqnarray, which is deprecated and can produce bad horizontal spacing.

\documentclass{article}

\usepackage{amsmath}

\begin{document}

\begin{alignat*}{2} 12 \left( \frac{1}{4}(2x-1)-x \right) &<12 \left( \frac{x}{6}-\frac{1}{3} \right) & \qquad \leftarrow\enspace & \text{multiplicar por 12} \\
-6x - 3 &< 2x -4 & \leftarrow\enspace & \text{simplificar} \\
(-6x - 3) - 2x &< (2x - 4) - 2x & \leftarrow\enspace & \text{restar }2x
\end{alignat*}

\end{document} 

enter image description here

3

Here are two ways:

  1. a regular align that uses the regular spacing parameters associated with spreading out multiple equations on the same line; and

  2. using a fixed-gap from the alignment operator. This requires you to set the RHS inside a zero-width box and inserting a fixed-width horizontal space that suits your needs.

enter image description here

\documentclass{article}
\usepackage{mathtools}
\newcommand{\insertbox}[1]{\fbox{\rule{#1}{\ht\strutbox}}}
\begin{document}

\begin{align*}
  \insertbox{50pt} & < \insertbox{30pt}
    && \text{Some text here} \\
  \insertbox{25pt} & < \insertbox{25pt}
    && \text{Some more text here} \\
  \insertbox{45pt} & < \insertbox{35pt}
    && \text{Some final text here}
\end{align*}

\begin{align*}
  \insertbox{50pt} & < \mathrlap{\insertbox{30pt}}
    \hspace{100pt}\text{Some text here} \\
  \insertbox{25pt} & < \mathrlap{\insertbox{25pt}}
    \hspace{100pt}\text{Some more text here} \\
  \insertbox{45pt} & < \mathrlap{\insertbox{35pt}}
    \hspace{100pt}\text{Some final text here}
\end{align*}

\end{document}

In both instances the \text{<text>} part is left-aligned. This should ensure proper alignment of any similar-sized symbols (like \leftarrow).

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