I have a very long equation. The MWE is:
\documentclass[12pt, A4paper]{article}
\usepackage{lipsum}
\usepackage{amsmath}
\usepackage[left=2cm, right=2cm, top=2cm,bottom=2cm]{geometry}
\begin{document}
\lipsum[1]
\begin{align*}
\sqrt{A^{2}+4B^{2}\times {PC^R}^{2}+4AB\times{PC^R}}&=\sqrt{\sigma_{11}+\sigma_{55}M_{1i,t}^2+\sigma_{77}M_{2i,t}^2+2\sigma_{15}M_{1i,t}+2\sigma_{17}M_{2i,t}+\sigma_{57}M_{1i,t}M_{2,it}} \\
&+\sqrt{4 PC^2\left[{\sigma_{22}+\sigma_{66}M_{1,it}^2+\sigma_{88}M_{2,it}^2+\sigma_{26}M_{1,it}+\sigma_{28}M_{2,it}+\sigma_{68}M_{1,it}M_{2,it}}\right]} \\
&+\sqrt{PC\left[\sigma_{12}+\sigma_{16}M_{1,it}+\sigma_{18}M_{2,it}+\sigma_{52}M_{1,it}+\sigma_{56}M_{1,it}^2+\sigma_{58}M_{1,it}M_{2,it}\right]}\\
&+\sqrt{PC\left[\sigma_{72}M_{2,it}+\sigma_{76}M_{2,it}M_{1,it}+\sigma_{78}M_{2,it}\right]}
\end{align*}
\lipsum[1]
\end{document}
As you can notice the equation reaches the end of the page. I know that I could try to make some simplifications or I could even split the RHS in more bits, but this are options that for some peculiar reasons are not useful to be followed.
Any suggestion on how I can shrink the equation and align it to the body text? Thanks in advance.
