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I have a Latex document as shown in the following image: (I am using AMS Math.)

what_i_have

I want to put a \implies sign just before the equation e=1. But, I do not want any other change to occur. I am aware of simple methods using align, but the problem is that they change the overall centring of the math block to something like this (NOT WANTED):

what_i_dont_want

What I want is something like this:

what_i_want

The code I am using is this:

\subsection{Definition}
A parabola is the set of points in a plane in such a way that their distance 
from a fixed point of the plane and from a fixed line of the plane are equal.
\begin{align*}
    &\mathrm{SP} = \mathrm{PM} \\
    \implies & e = 1
\end{align*}

What to do?

1 Answer 1

1

Use the \mathllap command, from mathtools:

\documentclass{article}
\usepackage[showframe]{geometry} 
\usepackage{mathtools}

\begin{document}

A parabola is the set of points in a plane in such a way that their distance
from a fixed point of the plane and from a fixed line of the plane are equal.
\begin{align*}
    &\mathrm{SP} = \mathrm{PM} \\
   \implies & e = 1
\end{align*}

\begin{align*}
    &\mathrm{SP} = \mathrm{PM} \\
    \mathllap{\implies} & e = 1
\end{align*}

\end{document} 

enter image description here

2
  • @KaranKaran: What do you mean? Using \mathllap, so that it is considered to have 0 width, or using the command \implies, or ... ?
    – Bernard
    Jun 8, 2017 at 8:35
  • 1
    In my opinion, it is not very good style. I would rather use a short sentence in ordinary language (therefore or something like that) introduced by ``intertext/\shortintertext`.
    – Bernard
    Jun 8, 2017 at 10:46

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