[Tex/LaTex] Coding F1 formula with mathtools

Question

I want to reproduce this formula. Note The 1 in the F should be subindex

This is my MWE which is not working for me:

%!TEX TS-program = xelatex
%!TEX encoding = UTF-8 Unicode

\documentclass{report}

\usepackage{mathtools}

\begin{document}
    \begin{itemize}
            \item \textbf{F1}. Conocido como el F-Score, se le denomina en estadística a la medida de precisión de un test. Resulta de la combinación de dos valores: precisión y exhaustividad. F=\frac{Precisión \times Exhaustividad}{Precisión + Exhaustividad}
        \end{itemize}
\end{document}

Additionaly, I don't know which format is better:

• F in italic or not
• · or x for multiplication
• the formula after the text or centering below it

Packages related with formulas in my .cls file are:

\RequirePackage[centertags]{amsmath}
\RequirePackage{mathtools}
\RequirePackage{amssymb}

Answer 1

\frac is only valid in math mode, so you want to either use inline math $ ... $ or displayed math for your equation. You make a subscript in math mode with an underscore, i.e. _{..}. Also, you want to use \text for the words in your fraction.

\documentclass{report}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage{mathtools}
\begin{document}
Inline math: $F_{1}=\frac{\text{Precisión} \times \text{Exhaustividad}}{\text{Precisión} + \text{Exhaustividad}}$

Or displayed math:
\[
F_{1}=\frac{\text{Precisión} \times \text{Exhaustividad}}{\text{Precisión} + \text{Exhaustividad}}
\]

\end{document}