I copy [this answer](https://tex.stackexchange.com/questions/232039/regular-polygon-and-tkz-euclide) and draw like this

```
\documentclass [border = 5mm] {standalone}
\usepackage{pgfplots}
\usepackage{tikz}
\usetikzlibrary{shapes.geometric,calc}
\begin{document}
\begin{tikzpicture}[line cap=round,line join=round,c/.style={circle,fill,inner sep=1pt},
	,declare function={k=6;}]
	
	\node[regular polygon,regular polygon sides=k,draw,minimum height=5cm] (a) at (0,0) {};
	\draw[red] let \p1=($(a.corner 1)-(a.center)$), \n1={veclen(\x1,\y1)} in circle (\n1);
	\foreach \x[count=\xi] in {A,B,...,F}{
		\node (a-\xi) at ([shift={({90+(\xi-1)*360/6}:3mm)}]a.corner \xi) {$\x$};
	}
	\pgfmathsetmacro{\k}{k}
	\draw[blue] let \p1=($(a.corner 1)-(a.center)$),
	\n1={veclen(\x1,\y1)*cos(360/\k/2} in circle[radius=\n1];
	
	\end{tikzpicture}
\end{document}
```

![image.png](/image?hash=72fb2927af6cd4d00dea67a1a31ddf1b45ad98e1246c562b2a2381413b5697a9)
Can I label `A, B, C`, ... automatically, not count like this `{A,B,...,W}`. Sometimes, with `n = 8`, I count by hand `A, B, C, D, E, F, G, H` and then {A,B,...,H}.