# Begin equation numbering with specific number

I would like to start my equations numbering with (8.67), so I used \setcounter{chapter}{7} but using \setcounter{equation}{66} does not help. How can I start equations numbering within chapter from number different than 1?

Here is more code:

\documentclass[12pt, c5paper]{book}
\usepackage{latexsym}%symbole do \LaTeXe
\usepackage{amsmath}
\usepackage{chngcntr}
\usepackage{polski}
\usepackage[utf8]{inputenc}
\numberwithin{equation}{chapter}
\begin{document}

\setcounter{chapter}{7}
\setcounter{equation}{66}

$$\label{eq1} \frac{i_{k}}{i_{p}}=\frac{1}{1,02+0471\surd\bar{a}/K\surd\bar{l}}$$

\end{document}

• What does not help help mean? What is the result? \setcounter{chapter}{8} and \setcounter{equation}{66} works for me – user31729 Nov 8 '15 at 18:49
• It means that I still get (8.1) instead of (8.67). – user2300369 Nov 8 '15 at 18:51
• Show us more of your code then -- are you using \setcounter{chapter}{7} before \chapter{foo} and \setcounter{equation}{66} as well? – user31729 Nov 8 '15 at 18:51
• I get (7.67), which is expected since chapter has the value of 7 then – user31729 Nov 8 '15 at 18:56
• Recall that the \chapter command resets equation, so you have to say \setcounter{equation}{66} after issuing \chapter. – egreg Nov 8 '15 at 19:01

This should work: \setcounter{equation}{66} after \chapter{...} since \chapter usually resets the equation counter.

\documentclass{book}

\begin{document}
\setcounter{chapter}{7}
\chapter{foo}   % chapter steps to 8 and resets equation to 1

\setcounter{equation}{66}
$$E = mc^2$$
\end{document}

• Setting \setcounter{chapter}{8} and omitting \chapter{foo} works too... – Mico Nov 8 '15 at 19:31