\begin{eqnarray*}
\vec{E}_{tot}=q\cdot k_{b}\cdot \dfrac{r}{r^3}\left\lgroup
\dfrac{\hat{r}-\left(\dfrac{d}{2\cdot r}\right)\hat{d}}{\left(1+\left(\dfrac{d}{2\cdot r}\right)^2-\left(\dfrac{d}{ r}\right)\hat{r}\cdot\hat{d}\cdot cos (\theta)\right)^{3/2}}-\dfrac{\hat{r}+\left(\dfrac{d}{2\cdot r}\right)\hat{d}}{\left(1+\left(\dfrac{d}{2\cdot r}\right)^2+\left(\dfrac{d}{ r}\right)\cdot\hat{r}\cdot\hat{d}\cdot cos(\theta)\right)^{3/2}}
\right\rgroup
\end{eqnarray*}
-
Welcome to TeX SX! Could you post a full compilable code?– BernardMay 25, 2017 at 16:33
5 Answers
This is a case for multline
:
\documentclass{article}
\usepackage{amsmath}
\begin{document}
\begin{multline*}
\vec{E}_{\mathrm{tot}}=
q\cdot k_{b}\cdot \dfrac{r}{r^3}
\left\lgroup
\frac{\hat{r}-\left(\dfrac{d}{2\cdot r}\right)\hat{d}}
{\biggl(1+\left(\dfrac{d}{2\cdot r}\right)^2-
\left(\dfrac{d}{r}\right)\hat{r}\cdot\hat{d}\cdot\cos(\theta)
\biggr)^{3/2}}
\right.
\\
\left.
{}-
\frac{\hat{r}+\left(\dfrac{d}{2\cdot r}\right)\hat{d}}
{\biggl(1+\left(\dfrac{d}{2\cdot r}\right)^2+
\left(\dfrac{d}{r}\right)\cdot\hat{r}\cdot\hat{d}\cdot\cos(\theta)
\biggr)^{3/2}}
\right\rgroup
\end{multline*}
\end{document}
I changed a couple of \left
-\right
pairs so to keep the outer parentheses a bit smaller.
First off: Don't use eqnarray
. Not now. Not ever.
Second, by getting rid of all \cdot
directives and replacing most \left
and \right
directives with smaller sizing opeators \Big
and \bigg
), and assuming normal-width margins, it's easily possible to write the entire equation on a single line.
Separately, you may want to look into not using displaymath-mode fractional notation. The result look is shown in the second equation of the following screenshot.
\documentclass[10pt,a4paper]{article}
\usepackage{amsmath,mleftright}
\newcommand\ddfrac[2]{\frac{\displaystyle #1}{\displaystyle #2}}
\usepackage[margin=2.5cm]{geometry} % choose page margins suitable
\begin{document}
\[
\vec{E}_{\mathrm{tot}}=q k_{b}^{} \frac{r}{r^3}
\left(
\ddfrac{\hat{r}-\Bigl(\frac{d}{2r}\Bigr)\hat{d}}{%
\biggl(1+\Bigl(\frac{d}{2r}\Bigr)^{\!2}
-\Bigl(\frac{d}{r}\Bigr)\hat{r}\hat{d}\cos(\theta)\biggr)^{\!3/2}}
-\ddfrac{\hat{r}+\Bigl(\frac{d}{2r}\Bigr)\hat{d}}{%
\biggl(1+\Bigl(\frac{d}{2r}\Bigr)^{\!2}
+\Bigl(\frac{d}{r}\Bigr)\hat{r}\hat{d}\cos(\theta)\biggr)^{\!3/2}}
\right)
\]
\bigskip
%% and now without displaystyle fractions
\[
\vec{E}_{\mathrm{tot}}=q k_{b}^{} \tfrac{r}{r^{3\mathstrut}}
\mleft[
\dfrac{\hat{r}-\frac{d}{2r}\hat{d}}{%
\bigl[1+\frac{d^2}{4r^{2\mathstrut}}
-\frac{d}{r}\hat{r}\hat{d}\cos(\theta)\bigr]^{3/2}}
-\dfrac{\hat{r}+\frac{d}{2r}\hat{d}}{%
\bigl[1+\frac{d^2}{4r^{2\mathstrut}}
+\frac{d}{r}\hat{r}\hat{d}\cos(\theta)\bigr]^{3/2}}
\mright]
\]
\end{document}
Since it is one equation, I would rather use the multline
(*) environment in this case.
\documentclass{article}
\usepackage{amsmath}
\begin{document}
\begin{multline*}
\vec{E}_{tot} = q\cdot k_{b}\cdot \dfrac{r}{r^3}\left\lgroup
\dfrac{\hat{r}-\left(\dfrac{d}{2\cdot r}\right)\hat{d}}{\left(1+
\left(\dfrac{d}{2\cdot r}\right)^2-\left(\dfrac{d}{ r}\right)\hat{r}
\cdot\hat{d}\cdot \cos (\theta)\right)^{3/2}}\right.\\
- \left.\dfrac{\hat{r}+\left(\dfrac{d}{2\cdot r}\right)\hat{d}}
{\left(1+\left(\dfrac{d}{2\cdot r}\right)^2
+\left(\dfrac{d}{ r}\right)\cdot\hat{r}\cdot\hat{d}\cdot \cos(\theta)
\right)^{3/2}}\right\rgroup
\end{multline*}
\end{document}
Your code is incorrect, since you use a blank line just before the end of eqnarray*
. Just remove that, then it works.
\documentclass{article}
\usepackage{amsmath,amsfonts,amssymb}
\begin{document}
\begin{eqnarray*}
\vec{E}_{tot}=q\cdot k_{b}\cdot \dfrac{r}{r^3}\left\lgroup
\dfrac{\hat{r}-\left(\dfrac{d}{2\cdot r}\right)\hat{d}}{\left(1+\left(\dfrac{d}{2\cdot r}\right)^2-\left(\dfrac{d}{ r}\right)\hat{r}\cdot\hat{d}\cdot cos (\theta)\right)^{3/2}}-\dfrac{\hat{r}+\left(\dfrac{d}{2\cdot r}\right)\hat{d}}{\left(1+\left(\dfrac{d}{2\cdot r}\right)^2+\left(\dfrac{d}{ r}\right)\cdot\hat{r}\cdot\hat{d}\cdot cos(\theta)\right)^{3/2}}
\right\rgroup
\end{eqnarray*}
\end{document}
Update: As alsways it is a bad idea to use eqnarray*
if there are such great environments as, f.i., align*
, which could btw help you break those equations.
\documentclass{article}
\usepackage{amsmath,amsfonts,amssymb}
\begin{document}
\begin{align*}
\vec{E}_{tot}&=q\cdot k_{b}\cdot \dfrac{r}{r^3}\left\lgroup
\dfrac{\hat{r}-\left(\dfrac{d}{2\cdot r}\right)\hat{d}}{\left(1+\left(\dfrac{d}{2\cdot r}\right)^2-\left(\dfrac{d}{ r}\right)\hat{r}\cdot\hat{d}\cdot \cos (\theta)\right)^{3/2}}\right.\\
&- \left.\dfrac{\hat{r}+\left(\dfrac{d}{2\cdot r}\right)\hat{d}}{\left(1+\left(\dfrac{d}{2\cdot r}\right)^2+\left(\dfrac{d}{ r}\right)\cdot\hat{r}\cdot\hat{d}\cdot \cos(\theta)\right)^{3/2}}\right\rgroup
\end{align*}
\end{document}
It can perfectly fit in a single line, if you remove the \cdot
s, which I think are unnecessary, and a number of useless parentheses. Unrelated to the problem at hand, I replaced \vec
, which isn't so nice with capital letters, with \vv
from esvect
:
\documentclass{article}
\usepackage{mathtools}
\usepackage{esvect}
\usepackage{showframe}
\renewcommand\ShowFrameLinethickness{0.3pt}
\begin{document}
\begin{equation*}
\vv*{E}{\text{tot}} =q k_{b}\, \frac{r}{r^3}\mkern-6mu%
\left\lgroup
\frac{\hat{r}-\dfrac{d}{2 r}\,\hat{d}}{\biggl(1+\biggl(\dfrac{d}{2 r}\biggr)^{\!2}\!-\dfrac{d}{ r}\,\hat{r}\hat{d}\,\cos \theta\biggr)^{\!\tfrac{3}{2}}}%
-\frac{\hat{r}+ \dfrac{d}{2 r}\,\hat{d}}{\biggl(1+\left(\dfrac{d}{2 r}\right)^{\!2}\!+\dfrac{d}{ r}\,\hat{r}\hat{d}\, \cos \theta \biggr)^{\!\tfrac{3}{2}}}
\right\rgroup
\end{equation*}
\end{document}
-
The use of
\!
in\biggr)^{\!2}
makes a big difference. IMO it improves the output too, by more closely associating the power with the bracket– Chris HMay 26, 2017 at 9:12