Theorems in a book

Question

I would like to write a theorem in the format of a book. So I write

\documentclass[12pt]{book}

but after that I write

\begin{theom}

and it does not compile. Can someone please help me write a theorem in a book?

Answer 1

As a start, I would suggest reading The Not So Short Introduction to LATEX2ε. It will give some idea of what LaTeX is all about and how to format a regular document.

Specific to your question, here is a small sample of what you might be after:

\documentclass[12pt]{book}
\newtheorem{theorem}{Theorem}
\begin{document}
\chapter{First chapter}
\section{First section}
This is some text, with the following theorem.
\begin{theorem}
My first theorem. \label{mytheorem}
\end{theorem}
Theorem~\ref{mytheorem} is pretty awesome.
\end{document}

Compiling this twice (to allow for appropriate referencing), you obtain:

If you're interested in numbering your theorem differently (say, having it reset with every \chapter and have the chapter number form part of the theorem number, as in chapter.theorem), you could use:

\newtheorem{theorem}{Theorem}[chapter]

The command breakdown as well as the meaning of the parameters is available from "Help with \newtheorem".

Specific theorem-formatting packages (like ntheorem or amsthm, say) are also available that might be of help. However, this depends on exactly what kind of formatting you're after.