\documentclass[tikz,border=5pt]{standalone}
\usepackage{amsmath}
\usepackage{amssymb}
\usepackage{xcolor}
\usepackage{tikz}
\newcommand{\LIGNE}[4]{
\draw[thick] (#1,#2) to (#3,#4);
}
\newcommand{\POINTILLE}[4]{
\draw[thick,dotted] (#1,#2) to (#3,#4);
}
\newcommand{\bSOM}[4]{
\node[scale=0.7,draw,circle,fill=black] at (#1,#2){};
\node[above] at (#1,#2+0.2){#3};
\node[below] at (#1,#2-0.2){#4};
}
\newcommand{\gSOM}[4]{
\node[scale=0.7,draw,circle,fill=lightgray] at (#1,#2){};
\node[above] at (#1,#2+0.2){#3};
\node[below] at (#1,#2-0.2){#4};
}
\begin{document}
\begin{tikzpicture}[scale=0.6]
\draw (0, 0) circle (4cm);
\node[rotate=-22] at (1,3.87) {\textbf{{\large $>$}}};
\node[rotate=-52] at (2.84,2.84) {\textbf{{\large $>$}}};
\node[rotate=-55] at (1.6,1.3) {\textbf{{\large $>$}}};
\node[rotate=-180] at (0,-2) {\textbf{{\large $>$}}};
\node[rotate=-140] at (2.85,-2.8) {\textbf{{\large $>$}}};
\LIGNE {0}{4}{3.5}{-2}
\LIGNE {3.5}{-2}{-3.5}{-2}
\POINTILLE{0}{4}{-3.5}{-2}
\POINTILLE {0}{4}{3.5}{-2}
\POINTILLE{0}{4}{-3.5}{-2}
\POINTILLE {3.5}{-2}{-3.5}{-2}
\POINTILLE {2}{3.5}{2}{-3.5}
\POINTILLE{2}{-3.5}{-4}{0}
\POINTILLE{2}{3.5}{-4}{0}
\POINTILLE {3.5}{2}{0}{-4}
\POINTILLE {-3.5}{2}{0}{-4}
\POINTILLE {3.5}{2}{-3.5}{2}
\POINTILLE {-2}{3.5}{4}{0}
\POINTILLE {-2}{3.5}{-2}{-3.5}
\POINTILLE {-2}{-3.5}{4}{0}
\bSOM{0}{4}{$2$}{}
\gSOM{2}{3.5}{\quad $0$}{}
\gSOM{3.5}{2}{\quad $0$}{}
\bSOM{4}{0}{ }{}
\node[color=black,thick]at(4.7,0){$2$};
\gSOM{3.5}{-2}{}{\quad $0$}
\gSOM{2}{-3.5}{}{\quad $0$}
\bSOM{0}{-4}{}{$2$}
\gSOM{-2}{-3.5}{}{ $0$ \quad }
\gSOM{-3.5}{-2}{}{}
\node[color=black,thick]at(-3.8,-2.5){$0$};
\bSOM{-4}{0}{ }{}
\node[color=black,thick]at(-4.7,0){$2$};
\gSOM{-3.5}{2}{}{ }
\node[color=black,thick]at(-3.9,2.5){$0$};
\gSOM{-2}{3.5}{$0$ \quad }{}
\node[below] at (0,-6){$(a): \sigma(f_1)= 8 $};
\draw (12, 0) circle (4cm);
\node[rotate=-22] at (13,3.87) {\textbf{{\large $>$}}};
\node[rotate=-52] at (14.84,2.84) {\textbf{{\large $>$}}};
\node[rotate=-35] at (13.8 ,3) {\textbf{{\large $>$}}};
\node[rotate=-90] at (15.5 ,0) {\textbf{{\large $>$}}};
\node[rotate=-145] at (13.8 ,-3) {\textbf{{\large $>$}}};
\node[rotate=145] at (10.2 ,-3) {\textbf{{\large $>$}}};
\node[rotate=90] at (8.5 ,0) {\textbf{{\large $>$}}};
\node[rotate=-90] at (15.5 ,0) {\textbf{{\large $>$}}};
\node[rotate=-80] at (15.9,1) {\textbf{{\large $>$}}};
\node[rotate=-110] at (15.85,-1) {\textbf{{\large $>$}}};
\node[rotate=-140] at (14.85,-2.8) {\textbf{{\large $>$}}};
\node[rotate=-165] at (13.2,-3.8) {\textbf{{\large $>$}}};
\LIGNE {12}{4}{15.5}{2}
\LIGNE {15.5}{-2}{15.5}{2}
\LIGNE {15.5}{-2}{12}{-4}
\LIGNE {8.5}{-2}{12}{-4}
\LIGNE {8.5}{-2}{8.5}{ 2}
\POINTILLE {14}{3.5}{16}{0}
\POINTILLE {14}{3.5}{10}{3.5}
\POINTILLE {15.5}{-2}{15.5}{ 2}
\POINTILLE {14}{-3.5}{10}{-3.5}
\POINTILLE {14}{-3.5}{16}{0}
\POINTILLE {8.5}{-2}{8.5}{ 2}
\POINTILLE {8.5}{-2}{12}{-4}
\POINTILLE {10}{-3.5}{8}{0}
\POINTILLE {10}{3.5}{8}{0}
\bSOM{12}{4}{$6$}{}
\gSOM{14}{3.5}{\quad $0$}{}
\gSOM{15.5}{2}{\quad $0$}{}
\gSOM{16}{0}{ }{}
\node[color=black,thick]at(16.7,0){$0$};
\gSOM{15.5}{-2}{}{\quad $0$}
\gSOM{14}{-3.5}{}{\quad $0$}
\gSOM{12}{-4}{}{$0$}
\gSOM{10}{-3.5}{}{ $0$ \quad \quad }
\gSOM{8.5}{-2}{}{}
\node[color=black,thick]at(8,-2.5){$0$};
\gSOM{8}{0}{ }{}
\node[color=black,thick]at(7.3,0){$0$};
\gSOM{8.5}{2}{}{ }
\node[color=black,thick]at(8.1,2.5){$0$};
\gSOM{10}{3.5}{$0$ \quad }{}
\node[below] at (12,-6){$(b): \sigma(f_2)=6$};
\end{tikzpicture}
\end{document}