# [Tex/LaTex] Vertical alignment of align* in enumerate

#enumeratealignlistsvertical alignment

Related (but not the same):
Align number from enumerate with equation
Displaying an equation in a list

Earlier today I asked a question about aligning equations in an enumerate environment and got an answer that seemed to work for the example I gave, but it turns out I wasn't really specific enough for my problem.

I'm using align* environments, often as the only part of a list item. (If you're wondering why I'm not using more words to introduce the align*, these are mostly homework solutions where most of the work is algebra, etc.)

Here's my code and what it makes (above the middle line):

\begin{enumerate}
\item \begin{align*}
x^2 + y^2 &= x^2 + (iy)^2 \\
&= (x + iy) (x - iy)
\end{align*}
\item \begin{align*}
\frac{1}{n^2-4} &= \frac14 \frac{4}{(n-2)(n+2)} \\
&= \frac14 \left( \frac{1}{n-2}-\frac{1}{n+2} \right)
\end{align*}
\end{enumerate}


I'm trying to make the baseline of the first line of the align* environment the same as the number's baselineâ€”I want the first line of the align* to have the same vertical position (centered horizontally in the same way) relative to its number as in the second half of my picture. (Side question: why is there so much space before the align* starts?)

I had been using Philippe Goutet's solution posted here, but have fairly recently found a simpler solution of using the aligned environment with the optional [t] alignment:

  \item \begin{aligned}[t] x^2 + y^2 &= x^2 + (iy)^2 \\ &= (x + iy) (x - iy) \end{aligned}


which yields:

## Code:

\documentclass{article}
\usepackage{showframe}
\usepackage{amsmath}

\begin{document}
\begin{enumerate}
\item \begin{aligned}[t] x^2 + y^2 &= x^2 + (iy)^2 \\ &= (x + iy) (x - iy) \end{aligned}
\item \begin{aligned}[t] \frac{1}{n^2-4} &= \frac14 \frac{4}{(n-2)(n+2)} \\ &= \frac14 \left( \frac{1}{n-2}-\frac{1}{n+2} \right) \end{aligned}
\end{enumerate}
\end{document}


If you want them horizontally centered as is the default with the align environment you could add an \hfill on either side:

  \item \hfill\begin{aligned}[t] x^2 + y^2 &= x^2 + (iy)^2 \\ &= (x + iy) (x - iy) \end{aligned}\hfill\null


## Code:

\documentclass{article}
\usepackage{showframe}
\usepackage{amsmath}

\begin{document}
\begin{enumerate}
\item \hfill\begin{aligned}[t] x^2 + y^2 &= x^2 + (iy)^2 \\ &= (x + iy) (x - iy) \end{aligned}\hfill\null
\item \hfill\begin{aligned}[t] \frac{1}{n^2-4} &= \frac14 \frac{4}{(n-2)(n+2)} \\ &= \frac14 \left( \frac{1}{n-2}-\frac{1}{n+2} \right) \end{aligned}\hfill\null
\end{enumerate}
\end{document}