Tick Marks in Geometry

Question

Here is an excerpt from my code:

\begin{tikzpicture}[scale=5.5]
    \coordinate[label=left:$A$]  (A) at (0,0);
    \coordinate[label=right:$B$]  (B) at (1,0);
    \coordinate[label=:$C$]  (C) at (0.5,0.866);
    \draw[] (A)--(B)--(C)--(A);
    \end{tikzpicture}

I want to denote AB=BC using the tick mark notation. Also, point C isn't exactly where it should be. How can I fix that? I rounded sqrt(3)/2 to 0.866. One last thing: I only want single tick marks.

Answer 1

Welcome to TeX.SE! You can add these marks with decorations.markings. Since you want two of them, it is shorter to use the .list key for that. Further, TikZ understands polar coordinates, and it also understands (0.5,{sqrt(3)/2}), so there is no need to unbury your calculator. ;-)

\documentclass[tikz,border=3.14mm]{standalone}
\usetikzlibrary{decorations.markings}
\begin{document}
\begin{tikzpicture}[scale=5.5,equal mark/.style={postaction={decorate,
decoration={markings,mark=at position #1 with {\draw (-2pt,-4pt) -- (-2pt,4pt);
\draw (2pt,-4pt) -- (2pt,4pt);}}}}]
    \coordinate[label=left:$A$]  (A) at (0,0);
    \coordinate[label=right:$B$]  (B) at (1,0);
    \coordinate[label=:$C$]  (C) at (60:1);
    \draw[equal mark/.list={1/6,1/2}] (A)--(B)--(C)--cycle;
\end{tikzpicture}
\end{document}  

As you can see, this code starts with \documentclass and ends with \end{document}, and is compilable.

And you may simplify/shorten the code using a \foreach loop.

\documentclass[tikz,border=3.14mm]{standalone}
\usetikzlibrary{decorations.markings}
\begin{document}
\begin{tikzpicture}[scale=5.5,equal mark/.style={postaction={decorate,
decoration={markings,mark=at position #1 with {\draw (-2pt,-4pt) -- (-2pt,4pt);
\draw (2pt,-4pt) -- (2pt,4pt);}}}}]
    \foreach \X/\Y in {210/A,-30/B,90/C} 
    {\coordinate[label=\X:$\Y$]  (\Y) at (\X:{1/sqrt(3)});}
    \draw[equal mark/.list={1/6,1/2,5/6}] (A)--(B)--(C)--cycle;
\end{tikzpicture}
\end{document}  

Answer 2

A PSTricks solution just for fun purposes.

\documentclass[pstricks,12pt,border=1cm]{standalone}
\usepackage{pst-eucl}
\begin{document}
\pspicture[MarkAngle=90](-4,4)
    \pstTriangle(4;150){C}(-4,0){A}(0,0){B}
    \pstSegmentMark{A}{B}
    \pstSegmentMark{B}{C}
\endpspicture
\end{document}

Bonus

\documentclass[pstricks,12pt,border=1cm]{standalone}
\usepackage{pst-eucl}
\begin{document}
\foreach \i in {90,100,...,170}{%
\pspicture[MarkAngle=90](-4,4)
    \pstTriangle(4;\i){C}(-4,0){A}(0,0){B}
    \pstSegmentMark{A}{B}
    \pstSegmentMark{B}{C}
\endpspicture}
\end{document}

Answer 3

one more tikz solution. for marks are used math symbol \| in nodes with option sloped placed on lines:

\documentclass[tikz,border=3.141592mm]{standalone}

\begin{document}
    \begin{tikzpicture}[scale=5.5]
\coordinate[label=left:$A$]     (A) at (0,0);
\coordinate[label=right:$B$]    (B) at (1,0);
\coordinate[label=$C$]          (C) at (0.5,0.866);
\draw (A) -- node {$\|$} (B) -- node[sloped] {$\|$} (C) -- (A);
    \end{tikzpicture}
\end{document}

now tikz version 3.1 in miktex works ...