With cellspace and adjustbox:
\documentclass[preview,border=12pt]{standalone}
\usepackage[a5paper, margin=5mm]{geometry}
\usepackage{amsmath}
\usepackage{array}
\usepackage[column=O]{cellspace}
\newcolumntype{M}[1]{>{\centering}O{m{#1}}}
\usepackage{adjustbox}
\begin{document}
{
\setlength\arraycolsep{0pt}
\setlength{\cellspacetoplimit}{4pt}
\setlength{\cellspacebottomlimit}{4pt}
\begin{tabular}{| c | Oc | c |}
\hline
\text{A pair of points}
& \text{Slope}
& Type \tabularnewline
\hline\hline
\adjustbox{valign=c,array=rrr} % <-------
{%
A( & 2, & -3)\
B( & -1, & 4)\
} & $\begin{aligned}
m & = \frac{y_B-y_A}{x_B-x_A}\
& = \frac{4-(-3)}{-1-2}\
& = -\frac{7}{3}
\end{aligned}$ & Decreasing \
\hline
\end{tabular}
}
\end{document}

or with makecell, tabularx and adjustbox:
\documentclass[preview,border=12pt]{standalone}
\usepackage[a5paper, margin=5mm]{geometry}
\usepackage{amsmath}
\usepackage{makecell, tabularx}
\newcolumntype{C}{>{\centering\arraybackslash}X}
\usepackage{adjustbox}
\begin{document}
\setlength\arraycolsep{0pt}
\setcellgapes{3pt}
\makegapedcells
\begin{tabular}{| C | C | C |}
\Xhline{1.2pt}
\text{A pair of points}
& \text{Slope}
& Type \tabularnewline
\Xhline{0.8pt}
\adjustbox{valign=c,array=rrr} % <-------
{%
A( & 2, & -3)\
B( & -1, & 4)\
} & $\begin{aligned}
m & = \frac{y_B-y_A}{x_B-x_A}\
& = \frac{4-(-3)}{-1-2}\
& = -\frac{7}{3}
\end{aligned}$ & Decreasing \
\Xhline{1.2pt}
\end{tabular}
\end{document}
or with booktabs and adjustbox:
\documentclass[preview,border=12pt]{standalone}
\usepackage[a5paper, margin=5mm]{geometry}
\usepackage{amsmath}
\usepackage{array, booktabs}
\usepackage{adjustbox}
\begin{document}
{
\setlength\arraycolsep{0pt}
\begin{tabular}{ c c c }
\toprule
\text{A pair of points}
& \text{Slope}
& Type \tabularnewline
\midrule
\adjustbox{valign=c,array=rrr} % <-------
{%
A( & 2, & -3)\
B( & -1, & 4)\
} & $\begin{aligned}
m & = \frac{y_B-y_A}{x_B-x_A}\
& = \frac{4-(-3)}{-1-2}\
& = -\frac{7}{3}
\end{aligned}$ & Decreasing \
\bottomrule
\end{tabular}
}
\end{document}
