6절 상호 참조 2

장
\chapter{저작}\label{chap:abc}
절
\section{상호 참조 2}\label{sec:abc}
수식
\begin{equation}\label{equ:abc}
    1 + 1 = 2
\end{equation}
\begin{equation}\tag{5.1} 1 + 1 = 2 \end{equation}
\[\tag{S}\label{equ:bcd}
    1 + 1 = 3
\]
\[\tag{S}\label{equ:bcd} 1 + 1 = 3 \]