equation Ax=b, inside matrix form

Question

I am trying to write a matrix form of Ax=b, just by putting every letter inside a matrix. The output is as I want, but I need to make it more readable, by increasing the size of the pmatrix with every letter in the center !

\begin{equation}
    \begin{pmatrix}
        A
    \end{pmatrix}
     \times
    \begin{pmatrix}
        x
    \end{pmatrix}
    =
    \begin{pmatrix}
        b
    \end{pmatrix}
\end{equation} 

Answer 1

I suppose you could increase the size of the parentheses by inserting typographic struts inside the \pmatrix environments, as is done in the third and fourth equations in the following screenshot.

You didn't specify just how tall the pmatrix-parentheses should be, but I trust that the ones generated by including either \tallstrut or \reallytallstrut are sufficiently tall.

\documentclass{article}
\usepackage{amsmath} % for 'pmatrix' environment
% define two tall typographic struts:
\newcommand\tallstrut{\vphantom{\tfrac{(}{(}}}
\newcommand\reallytallstrut{\vphantom{\dfrac{A}{A}}}

\begin{document}
\[
    \mathbf{Ax}=\mathbf{b} default (?) way of writing matrices and vectors
\qquad
    \begin{pmatrix} A \end{pmatrix} \times
    \begin{pmatrix} x \end{pmatrix} =
    \begin{pmatrix} b \end{pmatrix}
\qquad
    \begin{pmatrix} A\tallstrut \end{pmatrix} \times
    \begin{pmatrix} x\tallstrut \end{pmatrix} =
    \begin{pmatrix} b\tallstrut \end{pmatrix}
\qquad
    \begin{pmatrix} A\reallytallstrut \end{pmatrix} \times
    \begin{pmatrix} x\reallytallstrut \end{pmatrix} =
    \begin{pmatrix} b\reallytallstrut \end{pmatrix}
\]
\end{document}

Answer 2

Here's a solution using nicematrix and the Block macro.

MWE:

\documentclass{article}
\usepackage[T1]{fontenc}
\usepackage{nicematrix}

\begin{document}
\begin{equation*}
\begin{pNiceMatrix}[columns-width = 1em]
    \Block{3-3}<\LARGE>{A}\\
     & & \\
     & &
\end{pNiceMatrix}
\begin{pNiceMatrix}[columns-width = 1em]
    \Block{3-1}<\LARGE>{x}\\
    \ \\
    \ 
\end{pNiceMatrix}
=
\begin{pNiceMatrix}[columns-width = 1em]
    \Block{3-1}<\LARGE>{b}\\
    \ \\
    \ 
\end{pNiceMatrix}
\end{equation*}
\end{document}

Output: