Why doesn't newtxsf typeset all mathematical symbols in sans serif?

Question

I am looking for a nice sans serif math font to go with Fira Sans for beamer slides. I read the different suggestions in this post and found newtxsf to be the most fitting package. Indeed, it does look beautiful on lowercase greek letters, but for some reason, uppercase greek letters and numbers are still typeset in a serif font.

What am I doing wrong? Why doesn't the sans serif math package newtxsf change the shape of the uppercase greek letters and numbers?

\documentclass{beamer}

\usepackage{fontspec}
\usepackage{amsmath}
\setsansfont{Fira Sans}
\setmathrm{Fira Sans}
\setmathsf{Fira Sans}
\setmathtt{Fira Sans}
\usepackage{newtxsf}

\begin{document}
\frame{
Numbers outside of math mode: 12345.

Number in math mode: $12345$.

Capital letters in math mode: $AB\Gamma\Delta$.

Small letters in math mode: $\alpha\beta\gamma\delta$.}
\end{document}

Answer 1

I would suggest the Fira Math font. It obviously pairs well with Fira Sans. Here is an example (it works for me with lualatex but doesn't work with xelatex for some reason)

\documentclass{beamer}

\usepackage{fontspec}
\usepackage{amsmath}
\setmainfont{Fira Sans}
\setsansfont{Fira Sans}
\usepackage{unicode-math}
\setmathfont{Fira Math}

\begin{document}
\frame{
Numbers outside of math mode: 12345.

Number in math mode: $12345$.

Capital letters in math mode: $AB\Gamma\Delta$.

Small letters in math mode: $\alpha\beta\gamma\delta$.

Formula:
\[
  \int_0^1\frac{dx}{1+x^2}=\lim_{n\to\infty}\sum_{i=1}^n\frac{1}{1+(i/n)^2}.
\]
}
\end{document}

:

Answer 2

I must admit to not understanding the logic behind the instructions in the preamble of your document. The following, simpler setup would appear to work just fine:

\usepackage[no-math]{fontspec}
\setsansfont{Fira Sans}
\setmonofont{Fira Mono} % optional
\usepackage{newtxsf}

A full MWE (minimum working example):

Aside: If you wanted slanted rather than upright uppercase Greek letters, load newtxsf with the option slantedGreek. (uprightGreek is the default.) If, on the other hand, you want lowercase and uppercase Greek letters to be rendered using upright glyphs, load the newtxsf package with the option frenchmath.

\documentclass{beamer}
% \usepackage{amsmath} % is loaded automatically by 'beamer'
\usepackage[no-math]{fontspec}
\setsansfont{Fira Sans}
\usepackage{newtxsf}

\begin{document}
\begin{frame}
Numbers, text mode: 12345

Numbers, math mode: $12345$

Uppercase greek letters, math mode: $\Gamma\Delta\Psi\Omega$

Lowercase greek letters, math mode: $\gamma\delta\psi\omega$
\end{frame}
\end{document}