## LaTeX forum ⇒ Math & Science ⇒ box around just one equation inside align

Information and discussion about LaTeX's math and science related features (e.g. formulas, graphs).
kwicky
Posts: 2
Joined: Sun Mar 21, 2010 1:53 pm

### box around just one equation inside align

Hi,
I am using "\begin{align}..." to align two equations. I would like to put a box around the second equation only. However, "\boxed{...}" does not seem to work if the alignment character "&" is inside the "{}".

Thanks a lot,
Kai

daleif
Posts: 199
Joined: Wed Nov 19, 2008 12:46 am
As you have seen you cannot directly, but we can cheat a little (in the example memoir is not important, it is jut my standard class in emacs)

\documentclass{memoir}\usepackage{calc,amsmath}\newlength\dlf\newcommand\alignedbox[2]{   % #1 = before alignment   % #2 = after alignment   &   \begingroup   \settowidth\dlf{$\displaystyle #1$}   \addtolength\dlf{\fboxsep+\fboxrule}   \hspace{-\dlf}   \boxed{#1 #2}   \endgroup}\begin{document} \begin{align*}   f(x) &= a \\   \alignedbox{g(x)}{=5}\end{align*}\end{document}

It is the same kind of trick \MoveEqLeft from mathtools make use of

kwicky
Posts: 2
Joined: Sun Mar 21, 2010 1:53 pm
Daleif,

Brilliant, works perfectly!
Thanks a lot,

Kai