4

I would like to highlight the values for variables of a system of linear equations in the way shown in the picture below.

\begin{align*}
(IV) - (V) & \Rightarrow 4x_1 = 8 & \Rightarrow x_1 = 2 
\\ x_1 = \text{2 in (V):} & \Rightarrow 7 * 2 + 5x_2 = 34 & 
\Rightarrow x_2 = 4 \\ x_1 = \text{2 und } x_2 =  \text{4 in (II):} & 
\Rightarrow 3 * 2 + 4 + x_3 = 13 &\Rightarrow x_3 = 3
\end{align*}

This is the code I used, if its relevant.

How it should look like

  • Welcome to TeX.SX! Could you please make your example compilable? – TeXnician Nov 24 '17 at 6:51
9

Here a possible solution with a TikZ matrix of math nodes:

\documentclass{article}
\usepackage{amsmath,amssymb}
\usepackage{tikz}
\usetikzlibrary{matrix}

\begin{document}
\noindent Your example as a benchmark:
\begin{align*}
(IV) - (V) & \Rightarrow 4x_1 = 8 & \Rightarrow x_1 = 2 
\\ x_1 = \text{2 in (V):} & \Rightarrow 7 * 2 + 5x_2 = 34 & 
\Rightarrow x_2 = 4 \\ x_1 = \text{2 und } x_2 =  \text{4 in (II):} & 
\Rightarrow 3 * 2 + 4 + x_3 = 13 &\Rightarrow x_3 = 3
\end{align*}
My solution with a Ti\emph{k}Z matrix:
\begin{center}
\begin{tikzpicture}
    \matrix[matrix of math nodes,
        column 1/.style={nodes={anchor=east}},
        column 2/.style={nodes={anchor=west}},
        row sep=-.4ex
        ] (m) {
        (IV) - (V) &[-4pt] \Rightarrow 4x_1 = 8 &[30pt] \Rightarrow x_1 = 2 
        \\ 
        x_1 = \text{2 in (V):} & \Rightarrow 7 * 2 + 5x_2 = 34 & 
        \Rightarrow x_2 = 4 \\ 
        x_1 = \text{2 und } x_2 =  \text{4 in (II):} & 
        \Rightarrow 3 * 2 + 4 + x_3 = 13 &\Rightarrow x_3 = 3\\
    };
    \draw[red, line width=2pt] ([shift={(-4pt,2pt)}]m-1-3.north west) rectangle ([shift={(4pt,-2pt)}]m-3-3.south east);
\end{tikzpicture}
\end{center}
\end{document}

enter image description here

7

A solution with hf-tikz:

\documentclass{article}
\usepackage{amsmath}

\usepackage[customcolors]{hf-tikz}
\tikzset{offset def/.style={
        above left offset={-0.2,0.5},
        below right offset={0.35,-0.3},
    },
    color def/.style={
        offset def,
        set fill color=white,
        set border color=red,
    },
}


\begin{document}
\begin{align*}
  (IV) - (V) & \Rightarrow 4x_1 = 8 & \tikzmarkin[color def]{z}\Rightarrow x_1 = 2 
  \\ x_1 = \text{2 in (V):} & \Rightarrow 7 * 2 + 5x_2 = 34 & 
  \Rightarrow x_2 = 4 \\ x_1 = \text{2 und } x_2 =  \text{4 in (II):} & 
                                                                                                                                    \Rightarrow 3 * 2 + 4 + x_3 = 13 &\Rightarrow x_3 = 3\tikzmarkend{z}
\end{align*}

\end{document}

The result:

enter image description here

Check the package documentation for more options, including one to prevent the rounded corners.

4

Using tikz :

\documentclass[french]{article}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage{lmodern}
\usepackage{babel}

\usepackage{amsmath}

\usepackage{tikz}
\usetikzlibrary{fit}

\newcommand{\tikzmark}[2]{%
  \tikz[remember picture,baseline=(#1.base)]
  \node[text=black,anchor=center,inner sep=1pt] (#1) {#2};}

\begin{document}
\begin{align*}
  (IV) - (V) & \Rightarrow 4x_1 = 8 & \Rightarrow\tikzmark{a}{} x_1 = 2 
  \\ x_1 = \text{2 in (V):} & \Rightarrow 7 * 2 + 5x_2 = 34 & 
  \Rightarrow x_2 = 4 \\ x_1 = \text{2 und } x_2 =  \text{4 in (II):} & 
                                                                                                                                    \Rightarrow 3 * 2 + 4 + x_3 = 13 &\Rightarrow x_3 = \tikzmark{b}{} 3
\end{align*}

\tikz[overlay,remember picture]{
  \node[rectangle, draw=red,thick, minimum size=2cm ] at (barycentric cs:a=1,b=1) {};
}


\end{document}

enter image description here

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