added new dotproduct image

tikz/dot-product-3/dot-product-3.4.tex

@@ -0,0 +1,25 @@
+\documentclass{article}
+\usepackage{gensymb}
+\usepackage[pdftex,active,tightpage]{preview}
+\setlength\PreviewBorder{2mm}
+\usepackage{tikz}
+\usetikzlibrary{arrows,positioning,decorations.pathreplacing,shapes} 
+\tikzset{
+    %Define standard arrow tip
+    >=stealth',
+    % Define arrow style
+    pil/.style={
+           ->,
+           thick}
+}
+
+\begin{document}
+\begin{preview}
+\begin{tikzpicture}
+    \draw[fill=green!30, label=$a$] (0,0) -- node[above] {$\varphi$} (0.7,0)
+                        arc (0:120:0.7cm);
+    \draw[pil] (0,0) -- node[near end, above] {$\vec a$} (3cm, 0);
+    \draw[pil]  (0,0) -- node[near end, right] {$\vec b$} (120:2cm);
+  \end{tikzpicture}
+\end{preview}
+\end{document}