Alignment of equation numbering in amsbook

Question

I use \documentclass{amsbook}. When I add an equation within an enumeration, the equation number appears further to the left than the item number, which is not so pleasant. How to make the equation number aligned with the paragraph?

... (1) This is an item in the list

(1) x = y+z

I want it to be:

... (1) This is an item in the list

........ (1) x = y+z

Answer 1

You can accomplish that by putting your equation environment inside of a parbox of width \linewidth, as in

  \par\noindent\parbox{\linewidth}{
  \begin{equation}
    \label{eq:inner}
    x^{2} + y^{2} = z^{2}
  \end{equation}
  }

Inside of an enumeration (or any other list), the width of text used is \linewidth.

Answer 2

Inserting the align environment inside a minipage of width \linewidth blocks it into a specific width block:

\documentclass{amsbook}
\begin{document}
\noindent
\begin{minipage}[t]{.5\textwidth}
\begin{enumerate}
  \item This is an item in the list

  \begin{align}
    x=y+z
  \end{align}

  \item This is another item in the list
\end{enumerate}
\end{minipage}%
\begin{minipage}[t]{.5\textwidth}
\begin{enumerate}
  \item This is an item in the list

  \vskip\abovedisplayskip
  \noindent\begin{minipage}{\linewidth}
  \begin{align}
    x=y+z
  \end{align}
  \end{minipage}\par
  \vskip\belowdisplayskip

  \vskip\belowdisplayskip
  \item This is another item in the list
\end{enumerate}
\end{minipage}
\end{document}

Note that there might be some confusion in terms of the numbering display. Use the reqno document class option to avoid this. Alternatively, you might also consider using \tag to force the equation number to be something different.