# Equation caption format: Strange parenthesis?

I used a command to change the font family of my equation number, but it only affected the right parenthesis. The left one didn't change. What is going on? How do I fix this?

MWE:

\documentclass[12pt,a4paper]{article}
\usepackage{blindtext}
\usepackage{amsmath}
\renewcommand{\theequation}{\sffamily\footnotesize\bfseries\Alph{equation}}

\begin{document}
\blindtext
$$a^2 + b^2 = c^2$$
\end{document}


Example of error:

• What do you mean? The opening parenthesis is normal, and the closing parenthesis is boldface? – Bernard May 11 '18 at 18:35
• And what do you want, exactly? – Bernard May 11 '18 at 18:36
• you have (\theequation) so if you put a font change in \theequation then it will naturally only apply on one side (but you shouldn't put formatting in \thezzz counter macros. – David Carlisle May 11 '18 at 18:42
• Ok - but is there now a better way to change the font of equation caption? – D5E May 11 '18 at 18:45

I don't know if this is the most correct way of doing this, but...

The macro that holds the format of the equation tag is \maketag@@@. The standard definition is \hbox {\m@th \normalfont #1}, where #1 is (\theequation).

\documentclass[12pt,a4paper]{article}
\usepackage{blindtext}
\usepackage{amsmath}
\makeatletter
\renewcommand{\theequation}{\Alph{equation}}
\renewcommand{\maketag@@@}[1]{\hbox {\m@th \sffamily\footnotesize\bfseries #1}}
\makeatother

\begin{document}
\blindtext
$$a^2 + b^2 = c^2$$

\end{document}


Here it is, with the \newtagform command from mathtools:

\documentclass[12pt,a4paper]{article}
\usepackage{blindtext}
\usepackage{mathtools}
\renewcommand{\theequation}{\Alph{equation}}
\newtagform{sans}{\sffamily\bfseries\footnotesize(})

\begin{document}

\usetagform{sans}
\blindtext
$$a^2 + b^2 = c^2$$

\end{document}