This may seem like a silly question but I can't seem to find something to tag a question asking a solution for an algebraic equation. There is a systems-of-equations tag, but its description seems to strongly imply that it should only be used for... ahem... a system with more than one equation.
Additionally, if none of these apply, you can consider tagging with real-analysis, complex-analysis, or diophantine-equations according to the domain in which you seek solutions. I think this would allow for almost all questions to have at least one applicable tag, which is probably the most important goal of your suggestion. Sure, these won't be the most descriptive tag, but a prospective algebraic-equation wouldn't carry a lot of information either.
Basically, I cannot imagine why someone would be specifically (un)interested in single equations (whereas systems-of-equations has ties with e.g. linear algebra). This strongly reduces the merits of having the tag, to the point where I don't see a virtue in having it.