LaTeX: the number of equations

We want the equation number to be (1.1)(2.4) in different sections in stead of (1)..(4), add

\numberwithin{equation}{section}

before \begin{document}, don't forget loading the amsmath package

If we want to start a equation number from a specified number, use:

\setcounter{equation}{3}

or

\addtocounter{equation}{1}If we want the style: (1-1), (2-4), use:

\renewcommand{\theequation}{\arabic{section}-\arabic{equation}}