circle-polercoordinate

\documentclass[]{standalone}

\usepackage[]{graphicx}

\usepackage{tikz}
\usepackage{pgfplots}
\pgfplotsset{compat=1.17}
\tikzset{>=latex}
\usetikzlibrary{arrows,arrows.meta}
\usepackage{steinmetz}
\newcommand*{\equal}{=}

\usepackage{tikz-3dplot}
\usetikzlibrary{decorations.markings}

\tikzset{->-/.style={decoration={
  markings,
  mark=at position #1 with {\arrow{>}}},postaction={decorate}}}

\begin{document}
  \begin{tikzpicture}[scale=2]
    \draw (0,0) circle [radius=1];
    \fill ({cos(pi/2 r)}, {sin(pi/2 r)}) circle [radius=0.1] node[above=5pt] {1};
    \fill ({cos(pi/2 r - 1*2*pi/3 r}, {sin(pi/2 r - 1*2*pi/3 r)}) circle [radius=0.1] node[right=5pt] {2};
    \fill ({cos(pi/2 r - 2*2*pi/3 r}, {sin(pi/2 r - 2*2*pi/3 r)}) circle [radius=0.1] node[left=5pt] {3};
  \end{tikzpicture} 
\end{document}