documentclass[12pt,letterpaper]{article}
usepackage[a4paper,left=20mm,top=25mm,right=20mm,bottom=25mm]{geometry}
usepackage[utf8]{inputenc}
usepackage{amsmath}
begin{document}
Asymptotic equation of Motion
begin{align*}
mathcal{L}_n (nabla_{mu} n_{nu}) &=& n^{alpha} nabla_{alpha} (
nabla_{mu} n_{nu}) + nabla_{alpha} n_{nu} nabla_{mu} n^{alpha} +
nabla_{mu} n_{alpha} nabla_{nu} n^{alpha} \
&=& n^{alpha} nabla_{alpha} ( nabla_{mu} n_{nu}) - n^{alpha}
nabla_{mu} ( nabla_{alpha} n_{nu}) + n^{alpha} nabla_{mu} (
nabla_{alpha} n_{nu}) + nabla_{alpha} n_{nu} nabla_{mu} n^{alpha} +
nabla_{mu} n_{alpha} nabla_{nu} n^{alpha}
end{align*}
end{document}