# How to align text to the right in math mode?

I have a table of formulas, some have a description next to them, I want the equations to appear left flush and the text between parentheses right flush. I was writing it in the following way.

\documentclass[letterpaper,10 pt,twocolumn,fleqn]{article}
\setlength{\columnsep}{2.5cm}
\usepackage[inner=2.5cm,outer=2.5cm,bottom=2.5cm,top=2.5cm,landscape]{geometry}
\usepackage{nopageno,array,graphicx,amsbsy,amsfonts}
\usepackage{amsmath}
\begin{document}
${\bf P} = \int_{t_i}^{t_f}{\bf F}\,dt = \Delta{\bf p}\mbox{\hspace{7mm} (Impulse) }$
$\frac{dA}{dt} = \frac{l}{2\mu}=cte \mbox{\hspace{7mm} (Kepler's Second Law) }$
\end{document}


but the alignment is different for each equation.

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Please make your code compilable, starting with \documentclass{...} and ending with \end{document}. That may seem tedious to you, but think of the extra work it represents for TeX.SX users willing to help you. Help them help you: remove that one hurdle between you and a solution to your problem. – Jubobs Sep 2 '13 at 18:45
You need to include your preamble. As it stands, your code does not produce flush left equations. I need to know how you are doing this in order to work out what the problem with \tag* is. – Ian Thompson Sep 2 '13 at 19:04

You can use \tag* from the amsmath package.

\documentclass{article}
\usepackage{amsmath}
\begin{document}
$\mathbf{P} = \int_{t_i}^{t_f}\mathbf{F}\,dt = \Delta \mathbf{p}\tag*{(Impulse) }$
$\frac{dA}{dt} = \frac{l}{2\mu}=cte \tag*{(Kepler's Second Law) }$
\end{document}


Note that \mathbf is preferable to \bf; see this question for more details.

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I tried this way but now the equations are not left flush. – Monica G Sep 2 '13 at 18:51
@MonicaG --- you didn't say anything about flush left equations! Perhaps you could edit your question to explain exactly what you want. – Ian Thompson Sep 2 '13 at 18:53
The complete document is \documentclass[letterpaper,10 pt,two column,fleqn]{article} \setlength{\columnsep}{2.5cm} \usepackage[inner=2.5cm,outer=2.5cm,bottom=2.5cm,top=2.5cm,landscape]{geometry} \usepackage{nopageno,array,graphicx,amsbsy,amsfonts} \usepackage{amsmath} \begin{document} [\frac{dA}{dt} = \frac{l}{2\mu}=cte \tag*{(Kepler's Second Law)}] .... \end{document} Now it display the equations left flush and tags right flush. – Monica G Sep 2 '13 at 19:30

Here's another approach, currently set up to use the full \textwidth.

\documentclass{article}
\newcommand\lreqn[2]{\noindent\makebox[\textwidth]{$\displaystyle#1$\hfill(#2)}\vspace{2ex}}
\begin{document}
\lreqn{\textbf{P} = \int_{t_i}^{t_f}\textbf{F}\,dt = \Delta\textbf{p}}{Impulse}
\lreqn{\frac{dA}{dt} = \frac{l}{2\mu}=cte }{Kepler's Second Law}

This is the paragraph that follow the list
\end{document}


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You could put it in a tabular environment

\documentclass{article}
\usepackage{array}
\def\extrarowheight{1.5em}
\let\ds\displaystyle
\begin{document}
\begin{tabular}{lr}
$$\textbf{P} = \ds\int_{t_i}^{t_f}\textbf{F}\,dt = \Delta\textbf{p}$$ & (Impulse) \\
$$\ds\frac{dA}{dt} = \ds\frac{l}{2\mu}=cte$$ & (Kepler's Second Law) \\
\end{tabular}
\end{document}


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You can use the align environment.

Here is an example.

Edit: I have compiled this into a minimal working example, as per request. This will compile using XeLaTeX. I compiled this on a Mac running the latest MacTex distribution, but I think this should compile on most systems with XeLaTeX.

Edit^2: A bunch of includes are redundant, for instance, the enumerate include. I have copied the preamble from LaTeX-it.


\documentclass[10pt]{article}
\usepackage[usenames]{color} %used for font color
\usepackage{amssymb} %maths
\usepackage{amsmath} %maths
\usepackage[utf8]{inputenc} %useful to type directly diacritic characters
\usepackage{mathspec}
\usepackage{xunicode}
\usepackage{xltxtra}
\setmainfont{Helvetica}
\setmathsfont(Digits,Latin,Greek){Helvetica}
\usepackage[margin=2in]{geometry}
\usepackage{enumerate}

\begin{document}
\begin{align}
\mathbf{P} = \int_{t_i}^{t_f}\mathbf{F}\,dt = \Delta \mathbf{p}\tag*{(Impulse) }
\end{align}

\end{document}


The align environment also gives you more fine grained control over the display of equations.

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