3

I am trying to create a system of equations with my calculation steps on the right side and a double underlined result.

I've decided to use NiceArray from the nicematrix package for the calculation steps, which has given me the intended outcome.

I guess there is a very simple way of underlining my result using nicematrixand Tikz. Unfortunately I have no experience with Tikz.

What do I have to write in order to double underline my result?

I was searching many hours for a solution to fix both of my problems (calculation steps and double underlining) and finally I think I am very close to the solution.

\documentclass{scrartcl}
\usepackage{mathtools}
\usepackage{nicematrix}

\begin{document}

\begin{equation*}
\begin{NiceArray}{RCLL}
-2x + 72 & = & 18 - 7x  &\quad | - 7x \\
-9x + 72 & = & 18 & \quad | -72 \\
-9x & = & -54  & \quad | : (-9) \\
x & = & 6
\end{NiceArray}
\end{equation*}

\end{document}

enter image description here

  • Under which row does this double underline occur, and what is its full left/right extent? Welcome to the site. – Steven B. Segletes May 8 at 17:16
  • 3
    Shhh. I won't tell anyone, but the 2nd line does not follow mathematically from the first. – Steven B. Segletes May 8 at 17:17
  • I suppose adding \\\hline\hline to the end of the NiceArray is not what you are looking for? – Steven B. Segletes May 8 at 17:22
  • This looks like it might be what you were looking for tex.stackexchange.com/questions/249616/… – Benjamin Compson May 8 at 17:26
  • 1
    @StevenB.Segletes \\\hline\hline creates a line beneath the whole Array, which is not, what I suppose to do. @Benjamin Compson That answer creates a double underline but does not help me for my calculation steps, because I cannot use \underline for more than one column of the array. – Karl May 8 at 17:32
6

I'd go with array, with a special purpose command:

\documentclass{scrartcl}

\usepackage{mathtools}
\usepackage{array}

\newcommand{\ssep}{\lvert\;}
\newcommand{\result}[2]{%
  \mathrlap{\underline{\underline{\mathstrut\hphantom{#1=#2}}}}%
  #1 & = & #2%
}

\begin{document}

\begin{equation*}
\setlength{\arraycolsep}{0pt}
\begin{array}{r >{{}}c<{{}} l @{\quad} l}
-2x + 72 & = & 18 + 7x  & \ssep -7x \\
-9x + 72 & = & 18       & \ssep -72 \\
-9x & = & -54           & \ssep \mathbin{:}(-9) \\
\result{x}{6} \\
\end{array}
\end{equation*}

\end{document}

enter image description here

Alternatively, with aligned:

\documentclass{scrartcl}

\usepackage{mathtools}

\newcommand{\ssep}{\lvert\;}
\newcommand{\result}[2]{%
  \mathrlap{\underline{\underline{\mathstrut\hphantom{#1=#2}}}}%
  #1 & = #2%
}

\begin{document}

\begin{equation*}
\begin{aligned}
-2x + 72 & = 18 + 7x  && \ssep -7x \\
-9x + 72 & = 18       && \ssep -72 \\
-9x      & = -54      && \ssep \mathbin{:}(-9) \\
\result{x}{6}
\end{aligned}
\end{equation*}

\end{document}

enter image description here

With a fancier highlighting:

\documentclass{scrartcl}

\usepackage{mathtools}
\usepackage{hf-tikz}

\newcommand{\ssep}{\lvert\;}

\begin{document}

\begin{equation*}
\begin{aligned}
-2x + 72 & = 18 + 7x  && \ssep -7x \\
-9x + 72 & = 18       && \ssep -72 \\
-9x      & = -54      && \ssep \mathbin{:}(-9) \\
\tikzmarkin{r}x&=6\tikzmarkend{r}
\end{aligned}
\end{equation*}

\end{document}

fancier

  • Using aligned is by far the most simple way and works perfectly for me. Thank you very much! – Karl May 8 at 17:41
4

with the nicematrix package (as you intended in your minimal working example -- mwe). lines for underline results are drawn with tikz added as code-after option of NiceArray:

\documentclass{scrartcl}
\usepackage{nicematrix}

\begin{document}
    \[\setlength\arraycolsep{1.2pt}  % <--- added
\begin{NiceArray}{RCLL}%
    [code-after={\tikz\draw[double, double distance=2pt, semithick]   % <--- added 
        ([yshift=-3]4-1.south west) -- ([yshift=-3]4-3.south east);}]
-2x + 72 & = & 18 - 7x  &\quad | - 7x \\
-9x + 72 & = & 18 & \quad | -72 \\
-9x      & = & -54  & \quad | : (-9) \\
x        & = & 6
\end{NiceArray}
    \]
\end{document}

enter image description here

or fit box around result (again with use tikz as at above solution):

\documentclass{scrartcl}
\usepackage{nicematrix}

\begin{document}
    \[\setlength\arraycolsep{1.2pt}    % <--- added
\begin{NiceArray}{RCLL}%
    [code-after={\tikz\node[draw=red, semithick, fit=(4-1) (4-3)] {};}] % <--- added
-2x + 72 & = & 18 - 7x  &\quad | - 7x \\
-9x + 72 & = & 18 & \quad | -72 \\
-9x      & = & -54  & \quad | : (-9) \\
x        & = & 6
\end{NiceArray}
    \]
\end{document}

enter image description here

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.