How continue an equation next line
I suggest using the multlined
environment from mathtools
to break the radicand . You also can choose not to break it, but to type in medsize (~80 % of \displaystyle) with the \mediummath
command from nccmath
. I took the opportunity to clean your code:
\documentclass[11pt,a4paper,twocolumn]{article}
\usepackage[utf8]{inputenc}
\usepackage{mathtools, nccmath}
\begin{document}
\begin{equation*}
\bigl| \dot{r} \bigr| =
\sqrt{\begin{multlined}[b] -\!\bigl(e^{-t} ( \cos t + \sin t )\bigr)^2 + \\ \bigl(e^{-t} (\cos t + \sin t)\bigr)^2 + \bigl(-e^{-t}\bigr)^2 \end{multlined}}
\end{equation*}
\begin{align*}
\bigl| \dot{r} \bigr| & =
\sqrt{\medmath{ -\!\bigl(e^{-t} ( \cos t + \sin t )\bigr)^2 + \bigl(e^{-t} (\cos t + \sin t)\bigr)^2 + \bigl(-e^{-t}\bigr)^2}} \\
& = \sqrt{ -\!\bigl(e^{-t} ( \cos t + \sin t )\bigr)^2 + \bigl(e^{-t} (\cos t + \sin t)\bigr)^2 + \bigl(-e^{-t}\bigr)^2}
\end{align*}
\end{document}
As the equation*
environment doesn't permit line breaks, consider using a multline*
environment. And, instead of creating a multi-line surd expression with a \sqrt
instruction, I suggest you use (...)^{1/2}
notation.
Two additional comments about your code: Do try to use \left
and \right
less frequently, and don't needlessly encase various terms in curly braces.
\documentclass[11pt,a4paper,twocolumn]{article}
\usepackage{amsmath} % for 'multline*' env.
\begin{document}
...
\hrule % just to illustrate column width
\begin{multline*}
| \dot{r} | = \bigl\{
- e^{-t} ( \cos t + \sin t )^{2} \\
+ e^{-t} ( \cos t + \sin t )^{2}
+ (-e^{-t})^{2} \bigr\}^{1/2}
\end{multline*}
\end{document}
If you are interested in a square root expression and not a power notation that Mico's answer provides, have a look at the following code:
\begin{equation*}
\left| \dot{r} \right| =
\sqrt{
\begin{aligned}
&{- \, {e}^{-t} \left( \cos t + \sin t \right)}^{2} \, + \, \\
&{{e}^{-t} \left( \cos t + \sin t \right)}^{2} \, + \, {(- \, {e}^{-t})}^{2}
\end{aligned}
}
\end{equation*}