Subscript with "in" in math presenter

Hello all,

I am using LibreOffice on Linux CentOS 7. I am creating a presentation with math formulas for physics lessons.

I need to express the ratio V_out / V_in . The problem is that it doesn’t allow me to use “in” and it replaces it with a question marked turned upside down. I suppose this is because “in” is a keyword in formulas.

How can I skip it out in order to have it printed ? I tried double quotations but it doesn’t work.

I really thank you very much. My best regards


Thanks a lot!! I tried to find out if there were already a similar question, before asking myself, but I wasn’t able to find it.
Thanks again. Cheers