Align left-aligned formula at two points

You can use \phantom to apply the appropriate spacing within the align environment to ensure that the y is aligned with the a and the = signs are also aligned. If you want this entire equation adjacent to the left margin you can use flalign.

enter image description here

Note:

  • Note the trailing & which is needed to get equation all the way to the left margin.

Code:

\documentclass{article}
\usepackage{amsmath}
%\usepackage[showframe]{geometry}% Uncomment to see margins

\begin{document}
\begin{flalign*}
                 a+b+c&=1 &\\% Need this trailing alignment char to get all the way left
    y\phantom{{}+b+c} &=2 &
\end{flalign*}
\end{document}

You can use "big fractions" also inside array; using the array package helps, so say

\usepackage{array}

in your preamble. Then you can use

\begin{array}{@{}>{\displaystyle}l@{}>{\displaystyle{}}l@{}}
a+b+c &= y           \\
y     &= \frac{2}{3}
\end{array}

just as a single (math) object that you can put anywhere you like. Adding \vphantom{\frac{2}{3}} before the \\ in the first row can help spacing.

enter image description here

For example, with

\begin{flalign*}
\begin{array}{@{}>{\displaystyle}l@{}>{\displaystyle{}}l@{}}
    a+b+c &= y           \vphantom{\frac{2}{3}}\\
    y     &= \frac{2}{3}
\end{array}
&&
\end{flalign*}

you'll get the object flush with the left margin.


Here's your answer

\begin{alignat*}{2}‎
&a+b+c&&=1\\‎‎
&y&&=2
\end{alignat*}

Explanation: align is an environment for shifting between left-aligned columns and right-aligned ones, so if you want your equation to be shown as a totally left-aligned one, you need to add an extra column between the left-aligned columns. In the above example, first & in each line makes a left-aligned column, if you delete this ones you'll get a right-aligned column. The second ampersands in each line make a right-aligned column but we don't need this column so we add a third column by adding an & after the last ampersands in each line. flalign is a variation of align that increases the space between columns so as to cover the line completely. alignat omits unnecessary spaces between the columns (the other difference between alignat and align is that the first one takes an argument which shows the number of the columns). Note that adding a * after each of these three, makes them untaged.

Tags:

Align

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