amsmath – How to Align Equals Signs Between Boxed and Unboxed Split Lines

alignmentboxes

I'm trying to figure out how to align the equals sign with the rest of the equals on the last line. Unfortunately, I get the offset alignment you can see in the image below. Any recommendations on how to get things aligned around the &= for the final line?

\usepackage{amsmath}
\usepackage{bm}
\makeatletter
\renewcommand{\boxed}[2][\fboxsep]{{
  \setlength{\fboxsep}{#1}\setlength{\fboxrule}{0.8}\fbox{\m@th$\displaystyle#2$}}}
\makeatother

\begin{equation*}
    \begin{split}
        26(x-14)-23(x-14)&=39\\
        26x-364-23x+322&=39\\
        3x-42&=39\\
        3x&=81\\
        \\
        \boxed[10]{\mathbf{\therefore x&=27}}
    \end{split}
\end{equation*}

Best Answer

\documentclass{article}
\usepackage{mathtools,bm,amssymb}
\begin{document}
\begin{align*}
   26(x-14)-23(x-14)&=39\\
   26x-364-23x+322&=39\\
   3x-42&=39\\
   3x&=81\\[2mm]
   \Aboxed{\bm{\therefore x}&\bm{=27}}
\end{align*}
\end{document}

Related Solutions

Boxes – Difference Between \framebox{$$} and \boxed{} in LaTeX

Package amsmath defines \boxed:

\newcommand{\boxed}[1]{\fbox{\m@th$\displaystyle#1$}}

\framebox and \fbox are just different interfaces for the same internal \@frameb@x, which actually makes the box. \framebox has more options.

Thus, the main difference between \framebox{$...$} and $\boxed{...}$ is that \boxed sets \displaystyle, whereas it had to be done manually in the former variant: \framebox{$\displaystyle ...$}.

Another difference appears, if \mathsurround is not zero. This space is set, when TeX enters and leaves inline math mode. It is intended as separation of math from the surrounding text. Inside the box it does not make sense and \boxed removes it by setting \mathsurround to zero by \m@th.

A test file, which illustrates the differences:

\documentclass{article}
\usepackage[T1]{fontenc}
\usepackage{lmodern}
\usepackage{amsmath}

\begin{document}
  \newcommand*{\vs}{\mathrel{\text{vs.}}}
  \begin{align*}
    \text{\ttfamily\string\framebox\{\$\dots\$\}} &\vs
    \text{\ttfamily\string\boxed\{\dots\}}
    \\
    \framebox{$\frac{123}{456}$} &\vs \boxed{\frac{123}{456}}
    \\
    \setlength{\mathsurround}{1em}\framebox{$X$} &\vs
    \setlength{\mathsurround}{1em}\boxed{X}
\end{align*}
\end{document}

A simulation of \boxed would be:

\framebox{%
  \setlength{\mathsurround}{0pt}%
  $\displaystyle ...$%
}

Align – Using Boxed and Align in MathJax

Here's a workaround that works with MathJax, but it's not pretty and might need additional tweaking depending on the MathJax implementation you're working with:

$$ 
\begin{align*}
2x+y &= 11 \\ 
3x &= 19 - 2y 
\; \llap{\mathrel{\boxed{\phantom{3x = 19 - 2y}}}}
\end{align*} 
$$

Here's what this would look like on math.stackexchange.com:

Edit: I boxed the wrong line by mistake, but one can accomplish the same thing for any line within an align block.

Best Answer

Related Solutions

Boxes – Difference Between \framebox{$$} and \boxed{} in LaTeX

Align – Using Boxed and Align in MathJax

Related Question