我有两个问题：如何左对齐方程系统？如何中间对齐（垂直）项目符号？
\documentclass{article}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage[italian]{babel}
\usepackage[
a4paper,
margin=15mm,
bindingoffset=2mm,
heightrounded,
]{geometry}
\usepackage{amsmath}
\usepackage{microtype}
\usepackage{xcolor}
\usepackage{varwidth}
\usepackage{enumitem}
\usepackage{hyperref}
\usepackage{enumitem}
\newif\ifodd
\oddtrue
\newcommand\odd{\oddtrue\item}
\newcommand\pair{\oddfalse\item}
\begin{document}
\begingroup\setlength{\fboxsep}{6pt}
\colorbox{white}{%
\begin{varwidth}[t]{\textwidth}
TRIGONOMETRIA
\begin{itemize}[leftmargin=*,label={\ifodd\color{black}\else\color{blue}\fi\textbullet}]
\odd $\sin^{2} \alpha + \cos^{2} \alpha = 1$
\pair \textcolor{blue}{$\tan \alpha = \dfrac{\sin \alpha}{\cos \alpha}$}
\odd $\sin \alpha + \beta = \sin \alpha \cos \beta + \sin \beta \cos \alpha$
\pair \textcolor{blue}{$\cos \alpha + \beta = \cos \alpha \cos \beta - \sin \alpha \sin \beta$}
\odd $\tan \alpha + \beta = \dfrac{\tan \alpha + \tan \beta}{1 - \tan \alpha \tan \beta}$
\pair \textcolor{blue}{$\sin \alpha - \beta = \sin \alpha \cos \beta - \sin \beta \cos \alpha$}
\odd $\cos \alpha - \beta = \cos \alpha \cos \beta + \sin \alpha \sin \beta$
\pair \textcolor{blue}{$\tan \alpha - \beta = \dfrac{\tan \alpha - \tan \beta}{1 + \tan \alpha \tan \beta}$}
\odd $\sec \alpha = \dfrac{1}{\cos \alpha}$
\pair \textcolor{blue}{$\dfrac{\sin^{2} \alpha}{\cos^{2} \alpha} + 1 = \tan^{2} \alpha + 1 = \sec^{2} \alpha$}
\odd \[ \cos 2\alpha =\begin{cases}
\cos^{2} \alpha - \sin^{2} \alpha\\
2 \cos^{2} \alpha - 1\\
1 - \sin^{2} \alpha
\end{cases}
\]
\end{itemize}
\end{varwidth}%
}\endgroup
\end{document}
方程系统是最后一个
