Trig exercise sketches with TikZ

Submitted by jakob on Tue, 12/04/2012 - 23:09

A useful TikZ macro \angleMark{A}{B}{C} for marking angles in a polygon. Supply three points (of type TikZ coordinate or node). The angle marking is drawn on the inside, and the actual angle (in degrees) is left in \pgfmathresult.

Note the style setting for the mark: angleMark/.style={fill=blue!20!white,draw=blue}. The size (diameter) of the mark can be supplied as an optional first argument, e.g. \angleMark[1cm]{A}{B}{C}.

\documentclass[a4paper,11pt]{scrartcl}
\usepackage[utf8]{inputenc}
 
\usepackage{tikz}
\usetikzlibrary{calc}
 
\makeatletter      
\newcommand{\angleMark}[4][.5cm]{%
    \pgfmathanglebetweenpoints{\pgfpointanchor{#3}{center}}
                              {\pgfpointanchor{#2}{center}}
    \let\my@angleA\pgfmathresult
    \pgfmathanglebetweenpoints{\pgfpointanchor{#3}{center}}
                              {\pgfpointanchor{#4}{center}}
    \let\my@angleB\pgfmathresult
    \pgfmathparse{int(abs(\my@angleA-\my@angleB))}
    \ifnum\pgfmathresult>180 
%     \node at ($(#2) + (-2,-2)$) {$\my@angleA , \my@angleB$};
      \pgfmathparse{int(\my@angleA-180)}
      \ifnum\pgfmathresult>0
	\pgfmathsetmacro\my@angleA{\my@angleA-360}
      \else
	\pgfmathsetmacro\my@angleB{\my@angleB-360}
      \fi
    \fi
    \filldraw[angleMark] (#3) -- ($(#3)!#1!(#2)$)
      arc (\my@angleA:\my@angleB:#1) -- cycle;
    % put the angle in \pgfmathresult
    \pgfmathparse{abs(\my@angleA-\my@angleB)} 
}
\makeatother 
\begin{document}
 
\begin{tikzpicture}
        [angleMark/.style={fill=blue!20!white,draw=blue}]
    \coordinate [label=left:$A$](A) at (0,0); 
    \coordinate [label=right:$B$](B) at (5,0);
    \coordinate [label=left:$C$](C) at (110:4);
    \coordinate [label=$D$] (D) at ($(C) + (12:6)$);
    \draw (B) -- (A) -- (C) -- (D) -- (B) -- (C);
    \angleMark{B}{A}{C}
    % use \pgfmathresult for the label
    \node at ($(A) + (\pgfmathresult/2:1)$) 
      {$\pgfmathprintnumber[precision=0]\pgfmathresult^\circ$};
    \angleMark{C}{D}{B}
    \node at ($(D) + (\pgfmathresult/2-180:1)$) 
      {$\pgfmathprintnumber[precision=0]\pgfmathresult^\circ$};
    \angleMark{B}{C}{D}
    \node at ($(C) + (-10:1)$) 
      {$\pgfmathprintnumber[precision=0]\pgfmathresult^\circ$};
\end{tikzpicture}
 
\end{document}

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