%By Hammad Munawar (hammadmunawar.weebly.com) %Institute of Avionics and Aeronautics, Islamabad, Pakistan \documentclass[]{article} \begin{document} \begin{flushleft} \underline{\textbf{How to write long equations in LaTeX?}}\\ \vspace*{10pt} Here is a long equation: \begin{eqnarray} &y(k)=&a_{0}+a_{1}u(k-1)+a_{2}u^{2}(k-1)+b_{1}u(k-2)+b_{2}u^{2}(k-2) \nonumber\\ &&+c_{1}u(k-3)+c_{2}u^{2}(k-3)+d_{1}u(k-4)+d_{2}u^{2}(k-4)\nonumber\\ &&+e_{1}u(k-5)+e_{2}u^{2}(k-5) \end{eqnarray} \end{flushleft} \end{document}