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I am new in LaTeX, thus I need your help.

I want to align the \leq symbol under the + symbol. The problem is that the + symbol is contained inside a fraction, therefore, the \begin{aligned}--\end{aligned} environment, does not allow me to insert the & symbol inside this certain fraction.

How can I achieve this without having any problems?

An example:

$\displaystyle \begin{aligned}
\sqrt{\frac{2x}{y **&+** z}}+\sqrt{\frac{2y}{z+x}}+\sqrt{\frac{2z}{x+y}}\\
&\leq 3.
\end{aligned}$

P.S I have searched the site but I haven't found anything similar with my problem. (maybe I am not searching, right?)

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1  
Welcome to TeX.sx! –  Kurt Dec 5 '12 at 20:17

3 Answers 3

I would recommend a different approach and that is to use an \hphantom to insert the appropriate amount of horizontal space:

enter image description here

Notes:

  • I used \hphantom instead of \phantom as I did not want the vertical size of \sqrt{{\frac{2x}{y **}}} to affect the second row.
  • Alignment points located inside other terms such as \sqrt and frac are not usually this easy to do, and David's solution was quite clever in moving it outside and inserting a negative \hspace. I personally would never have thought of that as I tend to think of alignment form the left moving towards the right.

Code:

\documentclass{article}
\usepackage{amsmath}

\begin{document}

$\displaystyle \begin{aligned}
&\sqrt{\frac{2x}{y **+** z}}+\sqrt{\frac{2y}{z+x}}+\sqrt{\frac{2z}{x+y}}\\
&\hphantom{\sqrt{{\frac{2x}{y **}}}}\leq 3.
\end{aligned}$

\end{document}
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If you have some multline equation to typeset and you don't align globally by = or \leq, I would suggest you to try:

\begin{multline}
  f/i/r/s/t + l/i/n/e
\\
  \leq s/e/c/o/n/d + l/i/n/e
.\end{multline}

And surely you should use proper displayed equation and never ever do $\displaystyle. The env multline is provided by the package amsmath and you do not put it inside another environment (it is similar to equation). As well, it has a starred variant multline* that suppresses the numbering.

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2  
@George, while the other two answers do what you asked, you should accept this one, you don't need alignment here. –  David Carlisle Dec 5 '12 at 21:02

This is a seriously odd place to align, what mathematical meaning do you mean to convey by aligning the inequality with the + in the subterm?

However:

enter image description here

\documentclass{article}
\usepackage{amsmath}
\newlength\mlength

\begin{document}

\settowidth{\mlength}{$+**z$}
$\displaystyle \begin{aligned}
\sqrt{\frac{2x}{y **+** z}}&+\sqrt{\frac{2y}{z+x}}+\sqrt{\frac{2z}{x+y}}\\
&\hspace{-\mlength}\leq 3.
\end{aligned}$

\end{document}
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Hello. Thank you for you quick response. Well, I have some big Inequality expressions, and when I align them to center I must break them in 2 lines. But there is a problem at this point, since they exceed the paper size. –  George Dec 5 '12 at 20:10
    
Breaking into multiple lines is fine but aligning the <= with a + in a subterm makes no mathematical sense, the alignment is intended to align matching operators –  David Carlisle Dec 5 '12 at 20:47

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