documentclass{book}
usepackage{tikz,amsmath,amssymb,tkz-euclide}
    usetkzobj{all}
    usepackage{color}
usetikzlibrary{positioning}% To get more advances positioning options
usetikzlibrary{arrows}% To get more arrow heads
usepackage{amsthm,color}
usetikzlibrary{arrows,plotmarks}
usetikzlibrary{quotes,angles}


theoremstyle{definition}
newtheorem{exinn}{Example}[chapter]
newenvironment{example}
  {clubpenalty=10000
   begin{exinn}%
   mbox{}%
   {color{blue}leadershrule height .8ex depth dimexpr-.8ex+0.8ptrelaxhfill}%
   mbox{}linebreakignorespaces}
  {parkern2exhruleend{exinn}}

begin{document}
chapter{Chapter One}
section{Section One}

begin{tikzpicture}
  draw[blue, very thick]
    (0,0) coordinate (a) node[black,left] {A}
    -- (2,4) coordinate (b) node[black,above] {B}
    -- (7,0) coordinate (c) node[black,right] {C}
    pic["$alpha$", draw=orange, -, angle eccentricity=1.2, angle radius=1cm]
    {angle=a--b--c}
        pic["$beta$", draw=orange, -, angle eccentricity=1.2, angle radius=1cm]
    {angle=c--a--b}
        pic["$gamma$", draw=orange, -, angle eccentricity=1.2, angle radius=1cm]
    {angle=b--c--a}-- cycle;
end{tikzpicture}

end{document}