[Tex/LaTex] Equation line exceeds width of text block

Question

I have a problem with an equation which almost exceeds limits of the page. This is the code :

\documentclass[a4paper,12pt,blue,rgb,]{tubsbook}
\usepackage[utf8]{inputenc}
\usepackage[english]{babel}
\usepackage{lipsum}
\usepackage{listings}
\usepackage{color}
\usepackage{hyperref}
\usepackage{url}
\usepackage{array,multirow}
\newcommand\mcbf[1]{\multicolumn{2}{|c|}{\textbf{#1}}}
\newcommand\mlbf[1]{\multicolumn{2}{|l|}{\textbf{#1}}}
\usepackage{graphicx}
\usepackage[activate]{pdfcprot}

\begin{document}
\begin{center}
\begin{equation}
X[k1+4.k2]=\sum_{n2=0}^{N/4-1}[(x[n2]+(-i)^{k1}x[N/4+n2]+(-1)^{k1}x[N  /2+n2]+(i)^{k1}x[3N/4+n2])W_{N}^{k1.n2}]W_{N/4}^{k2.n2}
\end{equation}
\label{eqfft4}
\end{center}
\end{document}

and i get this result :

how can i fix that???

Answer 1

This is not really an issue of LaTeX formatting. If a formula is longer than the text width, it is hard to read and understand even if optimally typeset. I suggest to break down the formular by introducing abbreviations, e.g. in the following way. After that you can still decide to use some appropriate amsmath environment to align the equations.

\documentclass[a4paper,12pt]{scrbook}
\begin{document}
\begin{equation}
X[k1+4.k2]=\sum_{n2=0}^{N/4-1} \alpha(n2)\cdot W_{N}^{k1.n2}\cdot W_{N/4}^{k2.n2}
\label{eqfft4}
\end{equation}
where
\begin{equation}
\alpha(n2)= x[n2]+(-i)^{k1}x[N/4+n2]+(-1)^{k1}x[N  /2+n2]+(i)^{k1}x[3N/4+n2]
\end{equation}
\end{document}