[Tex/LaTex] Two equations with same label

Question

I have to translate a dissertation to a researcher. There is a problem I couldn't solve. Namely, there is an introduction chapter where the author has named an equation as (A). Then in the chapter one there is again an equation named as (A). Those equations are not the same in sense that first one has parameter z but another has parameter e^z. So how can I name two different equations with the same label? For example

e^{ix}+1=0 (A)

and

$e^{iy}=-1$ (A)

Answer 1

If you are using the amsmath package, you can specify the displayed label using the \tag macro:

\documentclass{article}
\usepackage{amsmath}

\begin{document}
    \begin{equation}\tag{A}
        e^{ix}+1=0
    \end{equation}
    \begin{equation}\tag{A}
        e^{iy}+1=0
    \end{equation}
\end{document}