答案1
像这样:
在图像中被视为 $sin{alpha} ~ \alpha$(在较小的 \alpha 时)并且轨迹中孔的角度之比约为 8:
\documentclass[tikz,
border=3mm,
]{standalone}
\usetikzlibrary{arrows.meta, decorations.markings}
\begin{document}
\begin{tikzpicture}[>=Straight Barb,
decoration={markings,% switch on markings
mark=between positions 0.2 and 0.8 step 0.25 with {\arrow[thick]{>}},
mark=at position 0.86 with {\arrow[thick]{>}},
mark=at position 0.98 with {\arrow[thick]{>}}
}]
% curve
\draw[fill=gray!10, postaction={decorate}]
(47.5:2) arc (47.5:360:2 ) arc (0:42.5:2)
-- + (225:0.5) arc (25 :0 :0.25) arc(360:65:0.25) -- cycle;
% singularity
\fill[red] (45:1.25) circle (1pt) node[inner sep=2pt,font=\footnotesize,right] {$a$};
% radius
\draw[thick, ->] (0,0) -- node[sloped,above] {$r$} (330:2);
% coordinate axes
\draw[->] (-3,0) -- (3,0) node[right] {$\Re$};
\draw[->] (0,-3) -- (0,3) node[above] {$\Im$};
\end{tikzpicture}
\end{document}