I am relatively new working with LaTeX and I don't know how to solve this problem.

I have several equations that I wrote in a general form, but when writing them, I want to show that the general form is just a generalization for three specific formulas; i.e.

I have this

but I want to have this:

P.S: I could use the command tag like in this post Customize equation numbering for Equation environment?, but I have over 60 equations and I could not use the command tag for each line individually (Also, there could be multiple errors doing it manually) Can someone help me please?

My MWE is:

 \documentclass[a4paper,12pt]{article} \usepackage[spanish]{babel} \usepackage[latin1]{inputenc} \usepackage{amsmath} \begin{document} \begin{equation} E=mc^2 \end{equation} \end{document}