How to make the letters under V bigger, I'm using 10pt on A5 paper in my original document and it's unreadable.
\documentclass{article}
\begin{document}
$V_{a bc defg}$
\end{document}
How to make the letters under V bigger, I'm using 10pt on A5 paper in my original document and it's unreadable.
\documentclass{article}
\begin{document}
$V_{a bc defg}$
\end{document}
You asked, "How to make the letters under V bigger"? I assume you mean, "as big as the letter V itself". If this assumption is correct, and if you also intend letters in subscript position to continue to be rendered in math-italic mode, you can use a \textstyle directive at the start of the subscript block; see the code below.
That said, it's typographic custom to typeset math-style subscript and superscript material ca 30% smaller than the material on the baseline (here: the single letter "V").
\documentclass{article}
\begin{document}
$V_{abcdefgVVV}$
$V_{\textstyle abcdefgVVV}$
\end{document}
in normalize and upright:
$V_{\mbox{a bc defg}}$
$V_{a bc defg}$. Please provide a more realistic example. – Mico Jan 13 '19 at 13:31