Displaying Equations in Specific Tabularx Environment

Question

I want to get rid of that huge blank space between the displayed equation and "converges to q". I am using a tabularx environment and hence I have to insert an enter (\\) after the displayed equation in order to make the table work properly. How can I get rid of that space?

Since I am working on a huge project and I cannot change the whole thing, I would appreciate if there is a solution that does not change the overall structure (tabularx, \hspace{3em}).

Here's my code.

\documentclass{article}
\usepackage[english]{babel}
\usepackage[a4paper,top=2cm,bottom=2cm,left=3cm,right=3cm,marginparwidth=1.75cm] 
{geometry}
\usepackage{amsmath}
\usepackage{amssymb}
\usepackage{amsthm}
\usepackage{enumitem}
\usepackage{graphicx}
\usepackage{xcolor}
\usepackage{indentfirst}
\usepackage{tabularx}
\usepackage{bm}
\usepackage{nicematrix}
\usepackage[colorlinks=true, allcolors=teal]{hyperref}
\usepackage[T1]{fontenc}
\begin{document}
\begin{tabularx}{0.9\linewidth}{l@{}c@{}X}
\hypertarget{5.5.1}{\textbf{5.5.1}} & $\quad$ & If $P$ is the transition matrix for a 
regular Markov chain, then :
\end{tabularx}
\renewcommand{\arraystretch}{1.5}
\begin{tabularx}{0.9\linewidth}{l@{}c@{}X}
& \hspace{3em} & (a) There is a unique probability vector $\mathbf{q}$ with positive 
entries such that \
& \hspace{3em} & \hspace{1.25em} $P \mathbf{p} = \mathbf{q}$. \
& \hspace{3em} & (b) For any initial probability vector $\mathbf{x}{0}$, the sequence 
of state vectors
$$ \mathbf{x}{0}, \quad P \mathbf{x}{0}, \quad \cdots, \quad P^{k} \mathbf{x}{0}, 
\quad \cdots $$ \
& \hspace{3em} & \hspace{1.25em} converges to $\mathbf{q}$. \
& \hspace{3em} & (c) The sequence $P, P^{2}, \cdots, P^{k}, \cdots$ converges to the 
matrix $Q$ each of whose \
& \hspace{3em} & \hspace{1.25em} column vectors is $\mathbf{q}$. \
\end{tabularx}
\end{document}

Answer 1

I think you're badly abusing the tabularx machinery, and you're engaging in a lot of hard-to-decipher (and, I hate to have to say it, fairly amateurish-looking) visual formatting.

I suggest you switch to a customized enumerate environment, along the following lines. A side benefit is that the excess virtual space issue you've encountered vanishes on its own.

\documentclass{article}
\usepackage[T1]{fontenc}
\usepackage[english]{babel}
\usepackage[a4paper, vmargin=2cm, hmargin=3cm,
            marginparwidth=1.75cm]{geometry}
\usepackage{amsmath,amssymb,amsthm}
\usepackage{enumitem}
\usepackage[colorlinks=true, allcolors=teal]{hyperref}
\newcommand\xzero{\mathbf{x}_{0}}
\begin{document}
\noindent
\hypertarget{5.5.1}{\textbf{5.5.1}} \quad
\begin{minipage}[t]{0.9\textwidth}
If $P$ is the transition matrix for a regular Markov chain, then:
\begin{enumerate}[label=(\alph*),left=0pt,align=left,itemsep=0pt]
\item There is a unique probability vector $\mathbf{q}$ with positive entries such that $P \mathbf{p} = \mathbf{q}$.
\item For any initial probability vector $\xzero$, the sequence of state vectors
[
\xzero, P \xzero, \dots, P^{k} \xzero
]
converges to $\mathbf{q}$.
\item The sequence $P, P^{2}, \dots, P^{k}, \dots$ converges to the  matrix $Q$, each of whose column vectors is~$\mathbf{q}$. 
\end{enumerate}
\end{minipage}
\end{document}