\documentclass[12pt]{report}
\usepackage[latin1]{inputenc}
\usepackage{amsmath}
\usepackage{amsfonts}
\usepackage{amssymb}
\usepackage[spanish]{babel}
\input{psfig.sty}
\begin{document}


\[
\lim_{n\rightarrow \infty} \left[ x\left( n\right) -x\left(
n-1\right) \right] =\lim_{n\rightarrow \infty}\frac{1}{n^{2}}%
=0
\]
\end{document}
