TiKZ 3.0 introduces angles
and quotes
libraries which simplifies this task.
A command like
\draw pic[draw] {angle=A--O--C};
will draw a sector line between line A--O
and O--C
with center at O
and anticlockwise. Sector radius is 5mm by default but can be changed with angle radius
parameter.
This sector line can be labelled with label
or with new quotes
syntax. The label is placed with certain angle eccentricity
(default = 0.6) which is a factor to be applied to angle radius
.
Next example is similar to student's code but using angle
pic.
\documentclass[border=2mm,tikz]{standalone}
\usetikzlibrary{angles,quotes}
\begin{document}
\begin{tikzpicture}
\coordinate[label=below left:O] (O) at (0,0); %
\coordinate[label=above right:A] (A) at (1,1); %
\coordinate[label=below right:B] (B) at (1,-1); %
\coordinate[label=above left:C] (C) at (-1,1);
\draw (C) -- (B); %
\draw (O) -- (A); %
\draw pic["$\cdot$", draw] {angle=B--O--A}
pic["$\cdot$", draw, angle radius=3mm, angle eccentricity=.25] {angle=A--O--C};
\end{tikzpicture}
\end{document}
