LaTeX-examples/tikz/triangle-angles/triangle-angles.tex

    \documentclass{article}
    \usepackage[pdftex,active,tightpage]{preview}
    \setlength\PreviewBorder{2mm}
    \usepackage{tikz}
    \usetikzlibrary{shapes, calc, shapes, decorations} 
    \usepackage{amsmath,amssymb}

    \begin{document}
    \begin{preview}
    \begin{tikzpicture}[thick]
        \newcommand\XC{4}
        \newcommand\ALPHA{30}

        \newcommand\XB{{(\XC*(cos(\ALPHA)*cos(\ALPHA) - sin(\ALPHA)*sin(\ALPHA)) + \XC)*0.5}}
        \newcommand\YB{{sqrt(cos(\ALPHA)*\XC*cos(\ALPHA)*\XC - (\XC*(cos(\ALPHA)*cos(\ALPHA) - sin(\ALPHA)*sin(\ALPHA)) + \XC)*0.5*(\XC*(cos(\ALPHA)*cos(\ALPHA) - sin(\ALPHA)*sin(\ALPHA)) + \XC)*0.5)}}

        \newcommand\XBo{{(\XB)+4}}
        \newcommand\YBo{{\YB}}
        \newcommand\XBp{{\XB*0.5}}
        \newcommand\YBp{{\YB*0.5}}

        % Draw the triangle
        \draw[fill=gray!10]  (0,    0) coordinate (A) 
            -- (\XB,\YB) coordinate (C) 
            -- (\XC,  0) coordinate (B) 
            -- (0,    0)  -- cycle;

        % Draw nodes
        \node at (A)[anchor=north] {A};
        \node at (B)[anchor=north] {B};
        \node at (C)[anchor=south] {C};

        % Draw edge text
        \node (c) at ($(A)!0.5!(B)$) [below] {c};
        \node (b) at ($(A)!0.5!(C)$) [above] {b};
        \node (a) at ($(B)!0.6!(C)$) [right] {a};


        % draw alpha
        \draw[fill=blue!30] (0,0) -- (0:0.75cm) arc (0:\ALPHA:.75cm);
        \coordinate[label=right:$\alpha$] (Alpha) at (0.25,0.15);

        % draw beta
        \begin{scope}[shift={(\XC, 0)}]
            \draw[fill=green!30] (0,0) -- (-180:0.50cm) arc (180:{180-(90-\ALPHA)}:0.5cm);
            \draw (150:0.35cm) node {$\beta$};
        \end{scope}

        % draw gamma
        \begin{scope}[shift={(\XB, \YB)}]
            \draw[fill=red!30] (0,0) -- ({180+\ALPHA}:0.5cm) arc ({180+\ALPHA}:{180+\ALPHA+90}:0.5cm);
            \draw (-0.1, -0.05) node[below] {$\gamma$};
        \end{scope}


        % shifted alpha
        \begin{scope}[shift={(4,0)}]
            \path[fill=blue!30] (0,0) -- (0:0.5cm) arc (0:\ALPHA:.5cm);
            \draw (0:0.5cm) arc (0:\ALPHA:.5cm);
        \end{scope}

        % shifted gamma
        \begin{scope}[shift={(4, 0)},rotate=180]
            \path[fill=red!30] (0,0) -- ({180+\ALPHA}:0.5cm) arc ({180+\ALPHA}:{180+\ALPHA+90}:0.5cm);
            \draw ({180+\ALPHA}:0.5cm) arc ({180+\ALPHA}:{180+\ALPHA+90}:0.5cm);
        \end{scope}

        \begin{scope}[shift={(3.13,-0.5)}]
            \draw[dashed, red] (0, 0)  -- (\XB,\YB);
        \end{scope}

        \draw[dashed, color=red] (-1, 0) -- (6, 0);
        \draw  (0,    0) coordinate (X) 
            -- (\XB,\YB) coordinate (Y) 
            -- (\XC,  0) coordinate (Z) 
            -- (0,    0);
    \end{tikzpicture}
    \end{preview}
    \end{document}