[Tex/LaTex] Make some equation numbers bold

boldequationsnumbering

I would like to make some equation numbers (that will be defined ad hoc) bold, while others are not. I can only figure out how to make all bold or unbold, not what I am looking for.

\documentclass[leqno]{book}
\usepackage{amsmath,amssymb,amsthm, amscd}
\usepackage[a4paper, textwidth=39cm, margin=1.2in, vmargin=3cm, marginparsep=20pt, marginparwidth=.6in,]{geometry} 
\usepackage{fancyhdr}
%\renewcommand\theequation{\bfseries\thesection.\arabic{equation}}
\begin{document}

\begin{equation}
x-y=z
\end{equation}

\begin{equation}
a+b=c
\end{equation}

\end{document}

Best Answer

As far as I am aware, the only way to do this is to keep on turning bold off and on every time that you want to do this. The cleanest solution would be to define a new version of equation that automatically makes the equation number bold:

\documentclass{article}
\begin{document}

\renewcommand\theequation{\thesection.\arabic{equation}}
\newenvironment{boldequation}{\renewcommand\theequation{\textbf{\thesection.\arabic{equation}}}\equation}
   {\endequation}

\begin{boldequation} 1+1=2 \end{boldequation}

\begin{equation} 1+1=2 \end{equation}

\end{document}

which gives:

enter image description here

Alternatively, a cruder way of doing this is using "switches" like:

\documentclass{article}
\begin{document}

\newcommand\boldequations{\renewcommand\theequation{\textbf{\thesection.\arabic{equation}}}}
\newcommand\normalequations{\renewcommand\theequation{\thesection.\arabic{equation}}}

\boldequations
\begin{equation} 1+1=2 \end{equation}

\normalequations
\begin{equation} 1+1=2 \end{equation}

\end{document}

The output is the same.

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