# triangle rule: Determinant of 3rd order

Could anybody help me to draw the picture with TikZ + PGF?

• Have you tried anything yet? If so you should add what you have done Jan 12 '16 at 12:47
• This looks overly complicated. Sarrus' rule is more intuitive. Jan 12 '16 at 12:50
• For me Sarrus' rule is overcomplicated) I found texample.net/tikz/examples/mnemonic-rule-for-matrix-determinant Jan 12 '16 at 12:56
• Welcome to TeX.SX! Long ago, I came to the conclusion that teaching such shortcuts for 3⨉3 matrices is simply a waste of time; these triangles are not easier to remember and to use than direct Laplace expansion. I myself use a personal version of Sarrus' rule, but I never teach it, because students will use it also for larger matrices, notwithstanding any warning the teacher can give. Jan 12 '16 at 12:57
• @egreg Computing determinants by hand is in general waste of time :) Jan 12 '16 at 13:03

As suggested in the comments, it is best to use the TikZ matrix library.

\documentclass{article}
\usepackage[T1]{fontenc}% for guillemets
\usepackage{tikz}
\usetikzlibrary{matrix}
\begin{document}
\begin{tikzpicture}
\matrix[matrix of nodes,left delimiter=|,right delimiter=|,
row sep=1em,column sep=1em,
nodes={draw,fill,circle,inner sep=1pt},nodes in empty cells] (m) at (0,0) {
& & \\
& & \\
& & \\
};
\draw (m-2-1) -- (m-3-2);
\draw (m-1-1) -- (m-3-3);
\draw (m-1-2) -- (m-2-3);
%
\draw (m-1-2) -- (m-3-1);
\draw (m-1-3) -- (m-3-2);
%
\draw (m-2-1) -- (m-1-3);
\draw (m-3-1) -- (m-2-3);

\matrix[matrix of nodes,left delimiter=|,right delimiter=|,
row sep=1em,column sep=1em,
nodes={draw,fill,circle,inner sep=1pt},nodes in empty cells] (n) at (5em,0) {
& & \\
& & \\
& & \\
};
\draw (n-2-3) -- (n-3-2);
\draw (n-1-3) -- (n-3-1);
\draw (n-1-2) -- (n-2-1);
%
\draw (n-1-2) -- (n-3-3);
\draw (n-1-1) -- (n-3-2);
%
\draw (n-2-3) -- (n-1-1);
\draw (n-3-3) -- (n-2-1);

\node at (0.0em,-2em) {<<$+$>>};
\node at (2.5em,0 |- m.base) {$,$};
\node at (5.0em,-2em) {<<$-$>>};
\end{tikzpicture}
\end{document}


• It's great, exactly Like I dreamed! So quickly, thank you. Jan 12 '16 at 13:12