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I normally write my solutions to mathematics problems in Latex using the begin/end{align*} feature.

How does one highlight an equation, or answer in my case, when the code is in begin/end{align*} ?

See my code below:

\begin{align*}
    %--
    i^7 &= 1 \times i^3 \\[5mm]
    %--
    i^7 &=  i^3 \\[5mm]
    %--
    i^7 &= i^2 \times i \\[5mm]
    %--
    i^7 &= -1 \times i \\[5mm]
    %--
    i^7 &=  -i \\[5mm]
    %--
    i^7 &=  -i
\end{align*}

So I would like to highlight the last line BUT maintain the alignment

Thanks

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7
  • Do you mean underline as the highlight as said in the title? (Well, it is easy to change its color just using \color{} within a {}.)
    – Teddy van Jerry
    Apr 25, 2022 at 4:32
  • Will \color{} maintain the alignment so that all the equal signs are under each other?
    – Stephan
    Apr 25, 2022 at 4:45
  • Here the last line you can use \color{red} i^7 & \color{red}=-i and it looks right. (No {} needed in align environment.)
    – Teddy van Jerry
    Apr 25, 2022 at 4:48
  • I tried your code and it gives me red text. I just want to highlight the the answer i^7 = -i.
    – Stephan
    Apr 25, 2022 at 4:56
  • SOmething like this works fine for me. \documentclass{article} \usepackage{xcolor} \usepackage{mathtools} % or \usepackage{amsmath} \begin{document} \begin{align*} %-- i^7 &= 1 \times i^3 \\[5mm] %-- i^7 &= i^3 \\[5mm] %-- i^7 &= i^2 \times i \\[5mm] %-- i^7 &= -1 \times i \\[5mm] %-- i^7 &= -i \\[5mm] %-- \color{red} i^7 & \color{red} =-i \end{align*} \end{document} Result: image
    – Teddy van Jerry
    Apr 25, 2022 at 4:57

1 Answer 1

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0

This problem can be concluded as colorbox inside align, so we can use

\documentclass{article}
\usepackage{xcolor}
\usepackage{mathtools}

% Reference: https://tex.stackexchange.com/a/13693/234654
\newlength\dlf
\newcommand\alignedbox[2]{
  % #1 = before alignment
  % #2 = after alignment
  &
  \begingroup
  \settowidth\dlf{$\displaystyle #1$}
  \addtolength\dlf{\fboxsep+\fboxrule}
  \hspace{-\dlf}
  \fcolorbox{yellow}{yellow}{$\displaystyle #1 #2$}
  \endgroup
}

\begin{document}
\begin{align*}
    %--
    i^7 &= 1 \times i^3 \\[5mm]
    %--
    i^7 &=  i^3 \\[5mm]
    %--
    i^7 &= i^2 \times i \\[5mm]
    %--
    i^7 &= -1 \times i \\[5mm]
    %--
    i^7 &=  -i \\[5mm]
    %--
     \alignedbox{i^7}{=-i}
\end{align*}
\end{document}

This genius idea is borrowed from here.

This method calculates the length before the aligned mark & into variable \dlf. Then \hspace is used to left shift the colorbox. Now the alignment is achieved.

RESULT

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