added gallery

documents/gallery/equilateral-triangle.tex

@@ -0,0 +1,37 @@
+\documentclass[varwidth=true, border=2pt]{standalone}
+\usepackage{tikz}
+\usetikzlibrary{positioning, calc}
+
+\begin{document}
+  \begin{tikzpicture}[scale=0.8]
+    % draw the background
+    \draw [line width=1.5pt, fill=gray!2] (0,0) -- (60:4) -- (4,0) -- cycle;
+
+    \coordinate[label=left:$A$]  (A) at (0,0);
+    \coordinate[label=right:$B$] (B) at (4,0);
+    \coordinate[label=above:$C$] (C) at (2,3.464);
+
+    \coordinate[label=below:$c$](c) at ($ (A)!.5!(B) $);
+    \coordinate[label=left:$b$] (b) at ($ (A)!.5!(C) $);
+    \coordinate[label=right:$a$](a) at ($ (B)!.5!(C) $);
+
+    % angle alpha
+    \draw[fill=green!30] (0,0) -- (0:0.75cm) arc (0:60:.75cm);
+    \draw (0.35cm,0.25cm) node {$\alpha$};
+
+    % angle beta
+    \begin{scope}[shift={(4cm,0cm)}]
+        \draw[fill=green!30] (0,0) -- (-180:0.75cm) arc (180:120:0.75cm);
+        \draw (150:0.5cm) node {$\beta$};
+    \end{scope}
+
+    % angle gamma
+    \begin{scope}[shift={(60:4)}]
+        \draw[fill=green!30] (0,0) -- (-120:.75cm) arc (-120:-60:.75cm);
+        \draw (-90:0.5cm) node {$\gamma$};
+    \end{scope}
+
+    % the triangle
+    \draw [line width=1.5pt] (A) -- (B) -- (C) -- cycle;
+  \end{tikzpicture}
+\end{document}