Well, from the practical point of view the equation type behaves much like a text only question.
But the difference is, that the result of the equation will be stored in your result database! As I understood your question, I assume that's exactly what you need.
And: yes you are right - the WYSIWYG editor is a little confusing. On the other hand an equation can be visible to your respondents (not always hidden in advanced settings). So you can, if you like, for example add images, audios or whatever you want with complex formulas and you will know what the respondent got.
To your convenience: simply edit the formula you need into the question field. Either in WYSIWYG mode or in source mode (I prefer source mode), don't forget the paranthesis, that's all.