3

I would like to have TikZ draw a triangle on the Cartesian plane - a triangle with vertices at the origin O, A = (2,1), and B = (-3, 5). I would also like to have two angles drawn and labeled - one from the positive x-axis to OA and one from the positive x-axis to OB. I would like the angles to have arrows where they touch OA and OB. I would also like to keep "\documentclass{amsart}" in the preamble.

5

Two simple possibilities using TikZ:

  1. For version 3.0, using the angles and quotes libraries:

    enter image description here

    The code:

    \documentclass{article}
    \usepackage{tikz}
    \usetikzlibrary{angles,quotes}
    
    \tikzset{
    mydot/.style={
      fill,
      circle,
      inner sep=1.5pt
      }
    }
    
    \begin{document}
    
    \begin{tikzpicture}[>=latex]
    % the coordinates of the vertices
    \coordinate (O) at (0,0);
    \coordinate (A) at (2,1);
    \coordinate (B) at (-3,5);
    \coordinate (E) at (2,0);
    
    % the axis
    \draw[help lines,->] (-3.5,0) -- (2.5,0);
    \draw[help lines,->] (0,-0.5) -- (0,5.5);
    
    % the edges of the triangle    
    \draw (O) -- (A) -- (B) -- cycle;
    
    % labelling the vertices
    \node[mydot,label={right:$A$}] at (A) {};
    \node[mydot,label={left:$B$}] at (B) {};
    \node[mydot,label={below:$O$}] at (O) {};
    
    % the arcs for the angles
    \path[gray]
      pic["$\alpha$" shift={(23pt,3pt)},draw,->,angle radius=1.5cm] {angle = E--O--A}
      pic["$\beta$" above=6pt,draw,->,angle radius=0.75cm] {angle = E--O--B};
    \end{tikzpicture}
    
    \end{document}
    
  2. For version 2.10, without libraries and using the arc path:

    enter image description here

    The code:

    \documentclass{amsart}
    \usepackage{tikz}
    
    \tikzset{
    mydot/.style={
      fill,
      circle,
      inner sep=1.5pt
      }
    }
    
    \begin{document}
    
    \begin{tikzpicture}[>=latex]
    % the coordinates of the vertices
    \coordinate (O) at (0,0);
    \coordinate (A) at (2,1);
    \coordinate (B) at (-3,5);
    
    % the axis
    \draw[help lines,->] (-3.5,0) -- (2.5,0);
    \draw[help lines,->] (0,-0.5) -- (0,5.5);
    
    % the edges of the triangle    
    \draw (O) -- (A) -- (B) -- cycle;
    
    % labelling the vertices
    \node[mydot,label={right:$A$}] at (A) {};
    \node[mydot,label={left:$B$}] at (B) {};
    \node[mydot,label={below:$O$}] at (O) {};
    
    % the arcs for the angles    
    \begin{scope}[gray]
    \draw[->] 
      (1,0) +(0:0.5cm) arc [radius=1cm,start angle=0,end angle=41] node[midway,right] {$\alpha$};
    \draw[->] 
      (0.5,0) +(0:0.25cm) arc [radius=0.75cm,start angle=0,end angle=122] node[midway,above] {$\beta$};
    \end{scope}
    \end{tikzpicture}
    
    \end{document}
    
  • we have angles lib for that now on version 3.00 ;) – percusse Jul 10 '14 at 17:35
  • @percusse really useful library. I've updated my answer. Thanks again. – Gonzalo Medina Jul 10 '14 at 18:04
  • 1
    @user143462 I don't see one question; I see five of them :) the mydot in the options of a node simply makes the node adopt the style that I previously defined for mydot (the node will be a filled circle of 3pt diameter). So, for example, \node[mydot,label={below:$O$}] at (O) {}; draws a small filled circle at the coordinate given by (O) (previusly defined to be at (0,0)) and places the label $O$ below the (O) coordinate. I'll continue in another comment (almost reached the word limit for this one). – Gonzalo Medina Jul 18 '14 at 1:59
  • 1
    (1,0) +(0:0.5cm) doesn't draw anything; it is the arc path which will do the drawing; a coordinate specified with a colon, uses polar coordinates: (<angle>:<length>), so (0:0.5) means 0.5 units at 0 degrees. Now, (1,0) +(0:0.5) is roughly equivalent to "move to (1,0) and then, from this point move 0.5 units in the direction given by 0 degrees" (see page 38 of the PGF manual for version 3.0 for a detailed explanation of the + and ++ modifiers). (continued) – Gonzalo Medina Jul 18 '14 at 2:09
  • 1
    @user143462 basically, (1,0) +(0:0.5) could be replaced by (1.5,0) I used the apparently more complex form just to have a better control over the drawing of the arc. – Gonzalo Medina Jul 18 '14 at 2:09

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.