Highlight or underline answer in Latex when code is in begin/end{align*}

Question

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

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 '22 at 04:32
Will \color{} maintain the alignment so that all the equal signs are under each other? — Stephan, Apr 25 '22 at 04:45
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 '22 at 04:48
I tried your code and it gives me red text. I just want to highlight the the answer i^7 = -i. — Stephan, Apr 25 '22 at 04:56
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 '22 at 04:57
I think your code changes the colour of the text. I would like to highlight the answer. — Stephan, Apr 25 '22 at 05:00

Teddy van Jerry · Accepted Answer · 2022-04-25T06:08:03.390

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.

Highlight or underline answer in Latex when code is in begin/end{align*}

1 Answers1