How to make the first line of equation level up with question number?

Question

I have a multi-line equation as follows:

\begin{enumerate}
\item
 \begin{enumerate}
 \item
  \begin{align*}
   A \cap (B \cup C)
    & =  x \in A \cap (B \cup C) \\
    & =  x \in A \wedge x \in (B \lor C)\\
    & =  x \in (A \wedge B) \lor x \in (A \wedge C) \\
    & =  x \in (A \cap B) \cup x \in (A \cap C) \\
    & =  (A \cap B) \cup (A \cap C)
  \end{align*}
 \end{enumerate}
\end{enumerate}

But I can't get the first line to level up with the question number (please see image below). How can I achieve that?

enter image description here

maybe this link help you http://tex.stackexchange.com/questions/58141/equations-inside-enumerate-aligned-on-items-number — Very23, Jul 08 '15 at 18:37
another question with useful content: Vertical alignment of align* in enumerate — barbara beeton, Jul 08 '15 at 18:43
Ist there a typo in the penultimate line? \cup instead of \cup x \in? The second and third line looks strange, too. — CampanIgnis, Mar 28 '17 at 17:01

score 0 · Answer 1 · answered Jul 08 '15 at 18:56

Do you want this?

\documentclass{article}
\usepackage{amsmath}

\newcommand\Item[1][]{% 
  \ifx\relax#1\relax  \item \else \item[#1] \fi
  \abovedisplayskip=0pt\abovedisplayshortskip=0pt~\vspace*{-\baselineskip}}

\begin{document}
\begin{enumerate}
\item \begin{enumerate}
       \Item   \begin{align*}
              A \cap (B \cup C)    & =  x \in A \cap (B \cup C) \\
              & =  x \in A \wedge x \in (B \lor C)\\
              & =  x \in (A \wedge B) \lor x \in (A \wedge C) \\
              & =  x \in (A \cap B) \cup x \in (A \cap C) \\
              & =  (A \cap B) \cup (A \cap C)
                 \end{align*}
     \end{enumerate}
\end{enumerate}

\end{document}

enter image description here

How to make the first line of equation level up with question number?

1 Answers1