\begin{document}
\section{}
\begin{align*}
\frac{1}{2}\times\sqr{a/l}\\
\frac{1}{2}\timesa/l^{\frac{1}{2}}\\
\frac{1}{2}\times\frac{a^{\frac{1}{2}}}{l}\\
1\times2^2\timesa^{\frac{1}{2}}\timesl\\
2^2\times\sqra\timesl\\
l=\frac{1}{2^2\timesa^{\frac{1}{2}}
\end{align*}
\end{document}