Enumere algumas seções do documento

Question

O resumo não deve ser enumerado, a lista de conteúdo deve começar com I (algarismos romanos) e o primeiro capítulo deve começar com 1 (números normais), como fazer?

\documentclass[11pt,letterpaper]{report}    
%\usepackage{etoolbox}
\usepackage{titlesec}

\begin{document}
{
\titleformat{\chapter}[block]{\filcenter\Huge\bfseries}{}{0pt}{}
\titlespacing{\chapter}{0pt}{0pt}{40pt}
\chapter*{ABSTRACT}
}

%\chapter*{\makebox[\linewidth]{ABSTRACT}}%\chapter*{\centering Abstract}
El principal mecanthis introthis introthis introthis introthis introthis introthis introthis introthis introthis introthis introthis introthis introthis introthis introthis introthis introthis introthis introthis introthis introthis introthis introthis introthis introthis introthis introthis intro

\section{Exp}
this Exp SECTION
\tableofcontents
\chapter{ETAPA2}
\label{cap:experimental}
this intro

\section{Exp2}
this Exp SECTION

\end{document}

Answer 1

Baseado emhttps://tex.stackexchange.com/a/408118/36296você poderia fazer algo assim:

\documentclass[11pt,letterpaper]{report}    
%\usepackage{etoolbox}
\usepackage{titlesec}

\newcommand\frontmatter{%
  \cleardoublepage
  % \@mainmatterfalse
  \pagenumbering{roman}
}

\newcommand\mainmatter{%
    \cleardoublepage
    % \@mainmattertrue
    \pagenumbering{arabic}
  }

\newcommand\backmatter{%
  \if@openright
    \cleardoublepage
  \else
    \clearpage
  \fi
  % \@mainmatterfalse
}


\begin{document}

{
\titleformat{\chapter}[block]{\filcenter\Huge\bfseries}{}{0pt}{}
\titlespacing{\chapter}{0pt}{0pt}{40pt}
\chapter*{ABSTRACT}
}
\thispagestyle{empty}
%\chapter*{\makebox[\linewidth]{ABSTRACT}}%\chapter*{\centering Abstract}
El principal mecanthis introthis introthis introthis introthis introthis introthis introthis introthis introthis introthis introthis introthis introthis introthis introthis introthis introthis introthis introthis introthis introthis introthis introthis introthis introthis introthis introthis intro

\section{Exp}
this Exp SECTION

\frontmatter
\tableofcontents

\mainmatter
\chapter{ETAPA2}
\label{cap:experimental}
this intro

\section{Exp2}
this Exp SECTION

\end{document}