# Set the counter for multiple equations of the same kind

I want equations (2) and (3) to be labeled as (1a) and (1b)

\documentclass[12pt,a4paper,table,usenames, dvipsnames]{book}
\usepackage[table]{xcolor}
\definecolor{def}{RGB}{66,103,178}
\usepackage{empheq}
\usepackage[most]{tcolorbox}
\newtcbox{\mymath}[1][]{%
nobeforeafter, math upper, tcbox raise base,
enhanced, colframe=blue!30!black,
colback=def!20, boxrule=1pt,
#1}

\begin{document}

Some text…
\begin{empheq}[box={\mymath[colback=Bittersweet!20]}]{equation}
(x-x_0)^2+(y-y_0)^2+(z-z_0)^2=R^2
\end{empheq}

Some text…
\begin{empheq}[box={\mymath[colback=Bittersweet!20]}]{equation}
x^2+y^2+z^2+Ax+By+C z=0
\end{empheq}

Some text…
\begin{empheq}[box={\mymath[colback=Bittersweet!20]}]{equation}
x^2+y^2+z^2=R^2
\end{empheq}

\end{document}

• Welcome to TeX SX! This is not clear at all. What would you like to have, precisely? – Bernard Jan 22 at 19:47
• Welcome to TeX.SX! As Bernard says it is not at all clear what you want to do. Further, can you please expand the code snippet that you have posted to a full minimal working example. A MWE should compile and be as small as possible to demonstrate your problem. it's much easier to help you if we have full working code to start from. – Andrew Jan 22 at 21:17
• environment subequations from asmath package is your friend – Zarko Jan 23 at 0:44
• Possible duplicate: How to reference equations using letters and numbers (due to the accepted answer) – Werner Jan 23 at 1:28

see if the following example gives what you looking for:

documentclass[12pt,a4paper,table,usenames, dvipsnames]{book}
\usepackage[table]{xcolor}
\definecolor{def}{RGB}{66,103,178}
\usepackage{empheq}% it call amsmath
\usepackage[most]{tcolorbox}
\newtcbox{\mymath}[1][]{%
nobeforeafter, math upper, tcbox raise base,
enhanced, colframe=blue!30!black,
colback=def!20, boxrule=1pt,
#1}

\begin{document}

Some text…
\begin{subequations}\label{eq:my equations}  % <---
\begin{empheq}[box={\mymath[colback=Bittersweet!20]}]{equation}
(x-x_0)^2+(y-y_0)^2+(z-z_0)^2=R^2
\end{empheq}

Some text…
\begin{empheq}[box={\mymath[colback=Bittersweet!20]}]{equation}
x^2+y^2+z^2+Ax+By+C z=0
\end{empheq}

Some text…
\begin{empheq}[box={\mymath[colback=Bittersweet!20]}]{equation}
x^2+y^2+z^2=R^2
\end{empheq}
\end{subequations} % <---

\end{document}
`
• That's exactly what I needed! – Dimitrios Sykias Jan 23 at 5:35
• @DimitriosSykias, than you can accept this answer with clicking on check mark at top left side of answer :-) – Zarko Jan 23 at 9:32