Here is one possible template you can extend. I tried to keep it pretty minimal while supporting the specific features you requested. It’s possible to get a lot fancier. This should be straightforward to add cards to, though.
\documentclass[12pt]{article}
% Sets up the geometry of each page to fit on one of your cards:
\usepackage[paperwidth=5in, paperheight=3in]{geometry}
% Supports the same color names as HTML and CSS:
\usepackage[svgnames, Svgnames, HTML]{xcolor}
% Loads amsmath plus some extra stuff.
\usepackage{mathtools}
% Enables modern, Unicode fonts:
\usepackage{unicode-math}
% Make all the fonts in the document match each other’s height:
\defaultfontfeatures{ Scale = MatchUppercase, Ligatures = TeX }
% I would not normally advise you to use a monospaced font as your main font,
% but if you want to, here is how:
\setmainfont{Anonymous Pro}[Scale = 1.0]
\setmonofont{Anonymous Pro}
% If you want to select a monospace font only some of the time, you might try
% the alltt package.
% You will also need a math font. This sets the letters in math mode to the
% same as your text font, and declares a fallback for the rest:
\setmathfont{GFS Neohellenic Math}
\setmathfont[range=up]{Anonymous Pro}
\setmathfont[range=it]{Anonymous Pro Italic}
\setmathfont[range=bfup]{Anonymous Pro Bold}
\setmathfont[range=bfit]{Anonymous Pro Bold Italic}
% You would declare your foreground and background colors here.
\begin{document}
\section*{\color{Navy}Trigonometric identities}
\begin{align*}
&\text{SOH} & &\text{CAH} \\
\sin^2 x &= 1 - \cos^2 x &
\cos^2 x &= 1 - \sin^2 x \\
\csc x &= \frac{1}{\sin x} &
\sec x &= \frac{1}{\cos x} \\
\sin (-x) &= - \sin x &
\cos (-x) &= \cos x
\end{align*}
\clearpage
\section*{\color{Navy}Law of Sines and Cosines}
\begin{itemize}
\item \( \frac{\sin \alpha}{\Alpha} =
\frac{\sin \beta}{\Beta} =
\frac{\sin \gamma}{\Gamma} \)
\item \( C^2 = A^2 + B^2 - 2AB \cdot \cos c \)
\end{itemize}
\end{document}
Because it uses modern, Unicode fonts, it will only compile with lualatex or xelatex.
Although I don’t demonstrate it here, as you wouldn’t be able to see it in the sample images, \nopagecolor sets the background transparent, and you can put \color{white} sets the foreground color. Both commands are from xcolor.
For Backward-Compatibility
Since you don’t have the anonymouspro package and seem to be restricted to PDFLaTeX, here is a version using legacy packages:
\documentclass[12pt]{article}
% Sets up the geometry of each page to fit on one of your cards:
\usepackage[paperwidth=5in, paperheight=3in]{geometry}
% Sets up the legacy 8-bit font encodings:
\usepackage[T1]{fontenc}
\usepackage{textcomp}
\usepackage[utf8]{inputenc} % The default since 2018.
% Loads some common math symbols. Mostly overwritten by newtx.
\usepackage{amssymb}
% Loads newtx math with newtxtt as the default text font:
\usepackage[ttdefault]{newtxtt}
\usepackage{newtxmath}
% Uses the text font for math symbols:
\usepackage{mathastext}
% Supports the same color names as HTML and CSS:
\usepackage[svgnames, Svgnames, HTML]{xcolor}
% Loads amsmath plus some extra stuff.
\usepackage{mathtools}
% If you need additional \mathscr, \mathcal, \mathfrak or \mathbb alphabets,
% consider loading mathalfa here. This template also would need to load some
% extra packages to support Greek.
% You would declare your foreground and background colors here.
\begin{document}
\section*{\color{Navy}Trigonometric identities}
\begin{align*}
&\text{SOH} & &\text{CAH} \\
\sin^2 x &= 1 - \cos^2 x &
\cos^2 x &= 1 - \sin^2 x \\
\csc x &= \frac{1}{\sin x} &
\sec x &= \frac{1}{\cos x} \\
\sin (-x) &= - \sin x &
\cos (-x) &= \cos x
\end{align*}
\clearpage
\section*{\color{Navy}Law of Sines and Cosines}
\begin{itemize}
\item \( \frac{\sin a}{A} =
\frac{\sin b}{B} =
\frac{\sin c}{C} \)
\item \( C^2 = A^2 + B^2 - 2AB \cdot \cos c \)
\end{itemize}
\end{document}
