Mathematical symbols- a thick bigger question mark

Question

I would need to get in Beamer presentation a thick bigger question mark. How is it possible to make it?

Answer 1

You could use the relsize package and its \larger command to scale up a bold-face question mark. In the following MWE, the default enlargement step is 1, but there's an option to change the amount of enlargement up to 5 (which corresponds to the \Huge absolute-size setting command).

The \bigqm ("big question mark") is set up using the \text command because you have the term "mathematical symbols" in your question's title; the macro also works in text mode, by the way.

\documentclass{beamer}
\usepackage{relsize}
\newcommand{\bigqm}[1][1]{\text{\larger[#1]{\textbf{?}}}}
\begin{document}
\begin{frame}

Question mark: ?

0 $x=y\bigqm[0]$

1 $x=y\bigqm$ 

2 $x=y\bigqm[2]$

3 $x=y\bigqm[3]$

4 $x=y\bigqm[4]$

5 $x=y\bigqm[5]$

\end{frame}
\end{document} 

Answer 2

\documentclass{beamer}

\begin{document}
\begin{frame}
What is your next question \scalebox{10}{\textbf{?}}
\end{frame}
\end{document}