2
    \documentclass[11pt,a4paper]{article}
    \usepackage{blindtext}
    \usepackage{mathtools}
    \usepackage{IEEEtrantools}

\begin{document}
\begin{IEEEeqnarray*}{rCl}
E&=&(ab)^{m}.\,\text{(Hypothesis).}
\\
&=&(ab)\times (ab)\times (ab)\times \dotsm m\,\text{factors}.\,\text{(Definition of an index).}
\\
&=&(a\times a\times a\times \dotsm m\,\text{factors}\times \\
&&(b\times b\times b\times \dotsm m\,\text{factors}.\,\text{(Laws of association and commutation).}
\\
E&=&a^{m}\times b^{m}.\,\text{(Definition of an index).}
\end{IEEEeqnarray*}
\end{document}
2

I'd use the AMS alignments, since you are loading the package anyway:

enter image description here

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

\setlength\mathindent{0pt}
\begin{document}
\noindent X\dotfill X
\begin{align*}
E&=(ab)^{m}.\,\text{(Hypothesis).}
\\
&=(ab)\times (ab)\times (ab)\times \dotsm m\,\text{factors}.\,\text{(Definition of an index).}
\\
&=(a\times a\times a\times \dotsm m\,\text{factors}\times \\
&(b\times b\times b\times \dotsm m\,\text{factors}.\,\text{(Laws of association and commutation).}
\\
E&=a^{m}\times b^{m}.\,\text{(Definition of an index).}
\end{align*}
\end{document}

Or perhaps

enter image description here

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

\setlength\mathindent{0pt}
\begin{document}
\noindent X\dotfill X
\begin{align*}
E&=(ab)^{m}\tag{Hypothesis}
\\[\jot]
&=\underbrace{(ab)\times (ab)\times (ab)\times \dotsm}_{m\,\text{factors}}\tag{Definition of an index}
\\[\jot]
&=\underbrace{( a\times a\times \dotsm)}_{ m\,\text{factors}}\times 
\underbrace{(b\times b\times \dotsm)}_{ m\,\text{factors}}\tag{Laws of association and commutation}
\\[\jot]
&=a^{m}\times b^{m}\tag{Definition of an index}
\end{align*}
\end{document}
  • To David, I have been waiting for an answer to proceed with my work. I shall be so grateful to you for providing me an answer. This works perfectly for me. :) – Nisal Kevin Kotinkaduwa Nov 4 '14 at 10:42
  • 1
    hmmm. the \times after \text doesn't have the correct spacing, but maybe because there's nothing after it. and there are a couple of unmatched left parens (although that was also the case in the original. and, finally, i think that the fourth line should be indented to the right of the equals sign; in the original it was lined up after the equals. (double && on the line after &=&). – barbara beeton Nov 5 '14 at 22:31
  • @barbarabeeton sorry, I'll sit at the back of the class, will edit;-) – David Carlisle Nov 5 '14 at 22:41
  • @barbarabeeton better? – David Carlisle Nov 5 '14 at 22:53
  • 1
    @NisalKevinKotinkaduwa see updated answer – David Carlisle Nov 5 '14 at 22:53

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