Multi horizontal alignment in mathmode

Question

I would like to realize an alignment like the following:

formulaformula1
formulaformulaformula2
           formula3
           formula4

So I would like formulaformula1 and formulaformulaformula2 to be left aligned, while formula3 and formula4 should be left aligned with a specific position in formulaformulaformula2.

Also I want to frame it with \fbox and put the box in the center.

Answer 1

Assuming that you want this in a displaymath format \[...\], then you might just as well insert the equation in an array since it allows for easy bordering:

\documentclass{article}
\usepackage{array}% http://ctan.org/pkg/array
\usepackage{lipsum}% http://ctan.org/pkg/lipsum
\begin{document}
\lipsum[1]
\[
  \renewcommand{\arraystretch}{1.5}%
  \begin{array}{|l|}
    \hline
    a_0+a_1x+a_2x^2=b_2y^2-b_1y-b_0 \\
    c_3z^3\times c_4z^4\times c_5z^5\times c_6z^6\geq a+b+c+d+e \\
    \phantom{c_3z^3\times c_4z^4\times{}}c_5z^5-9pq+b\ell\alpha h \\
    \phantom{c_3z^3\times c_4z^4\times{}}E=mc^2 \\
    \hline
  \end{array}
\]
\lipsum[2]
\end{document}

The goal here is to use \phantom{<stuff>} to duplicate <stuff> that you want to use as your alignment tool, but not typeset.

Answer 2

• For multi-line formulas with alignment, amsmath environments such as align are useful. For example, alignat* could be used for equations with multiple alignment places. These environments are appropriate for aligning at relation signs such as equal signs, because of consistent spacing around the relation signs.

• For boxing equations, the empheq package is useful. It offers amsmath support and various customizations.

Here's an example:

\documentclass{article}
\usepackage{amsmath}
\usepackage{empheq}
\begin{document}
\begin{empheq}[box=\fbox]{alignat*=2}
    &ax + by + c + {}&&x = 0 \\
    &ab = c &\\
    &&&x+y=z
\end{empheq}
\end{document}

The first two equations are left aligned, the third equation x is aligned with the x in the first equation. Alignment at equal signs is not even used yet.