我怎样才能将突出显示的文本左对齐到下一行？

Question

\documentclass[11pt,a4paper]{article}
\usepackage{blindtext}
\usepackage{mathtools}
\usepackage{amsmath}
\usepackage{IEEEtrantools}


\begin{document}
Proof:
\vspace{-1em}
\begin{IEEEeqnarray*}{rCl}
E&=&\times \underbrace{(\times a\times a\times a\times \dotsm)}_{m\,\text{factors}}\div \underbrace{(\times a\times a\times a\times \dotsm)}_{n\,\text{factors}};\,\text{(Definition of an index)}\\
&=&\times a\times a\times a\times \dotsm \times a \div a\div a\div a \dotsm \div a;\,\text{(The law of association for multiplication and division)}\\
&=&\times (\times a\times a\times a\times \dotsm m-n\,\text{factors})\\
&&\times (a\div a)\times (a\div a)\times \dotsm n\,\text{factors};\,\text{(The laws of commutation and association)}\\    
&=&\times \underbrace{(\times a\times a\times a\times \dotsm)}_{m-n\,\text{factors}};\,\text{(Properties of division)}\\
E&=&a^{m-n}.\,\text{(Definition of an index)}
\end{IEEEeqnarray*}
[![enter image description here][1]][1]\end{document} 

Answer 1

由于IEEEtranstools不是标准 LaTeX，我在下面显示时没有它。我只是将注释移到它自己的行，然后\rlap后面跟着一个幻影E。

根据需要，编辑添加额外的空组{}来制作二元运算符。\times

正如 Runar 在评论中指出的那样，如果没有IEEEtranstool，eqnarray下面显示的方法将不是首选，而是align的环境之一amsmath。因此，下面我展示了这两种方法。

\documentclass[11pt,a4paper]{article}
\usepackage{blindtext}
\usepackage{mathtools}
\usepackage{amsmath}
%\usepackage{IEEEtrantools}

\begin{document}
Proof:
\vspace{-1em}
%\begin{IEEEeqnarray*}{rCl}
\begin{eqnarray*}
E&=&\times \underbrace{(\times a\times a\times a\times \dotsm)}_{m\,\text{factors}}\div \underbrace{(\times a\times a\times a\times \dotsm)}_{n\,\text{factors}};\,\text{(Definition of an index)}\\
&=&{}\times a\times a\times a\times \dotsm \times a \div a\div a\div a \dotsm \div a;\\
 \rlap{(The law of association for multiplication and division)}\phantom{E}& \\
&=&{}\times (\times a\times a\times a\times \dotsm m-n\,\text{factors})\\
&&{}\times (a\div a)\times (a\div a)\times \dotsm n\,\text{factors};\,\text{(The laws of commutation and association)}\\    
&=&{}\times \underbrace{(\times a\times a\times a\times \dotsm)}_{m-n\,\text{factors}};\,\text{(Properties of division)}\\
E&=&a^{m-n}.\,\text{(Definition of an index)}
\end{eqnarray*}
%\end{IEEEeqnarray*}

\begin{align*}
E&=\times \underbrace{(\times a\times a\times a\times \dotsm)}_{m\,\text{factors}}\div \underbrace{(\times a\times a\times a\times \dotsm)}_{n\,\text{factors}};\,\text{(Definition of an index)}\\
&={}\times a\times a\times a\times \dotsm \times a \div a\div a\div a \dotsm \div a;\\
 \rlap{(The law of association for multiplication and division)}\phantom{E}& \\
&={}\times (\times a\times a\times a\times \dotsm m-n\,\text{factors})\\
&\phantom{{}={}}{}\times (a\div a)\times (a\div a)\times \dotsm n\,\text{factors};\,\text{(The laws of commutation and association)}\\    
&={}\times \underbrace{(\times a\times a\times a\times \dotsm)}_{m-n\,\text{factors}};\,\text{(Properties of division)}\\
E&=a^{m-n}.\,\text{(Definition of an index)}
\end{align*}
\end{document}