[Tex/LaTex] Changing the formatting of equation numbers

Question

How can I change equation numbering so that the chapter number is outside the parenthesis like this:

1(1)

instead of

(1.1)

Answer 1

You need to redefine \tagform@ from amsmath (to remove the outer parentheses) and \theequation (to add them in the desired location):

\documentclass{book}
\usepackage{amsmath}

\renewcommand\theequation{\thechapter(\arabic{equation})}
\makeatletter
\def\tagform@#1{\maketag@@@{\ignorespaces#1\unskip\@@italiccorr}}
\makeatother


\begin{document}

\chapter{Test Chapter}
\eqref{eq:test}
\begin{equation}\label{eq:test}
a=b.
\end{equation}

\end{document}