如何在 LaTeX 中制作括号？

Question

如何在 LaTeX 中制作下面的括号和公式？

Answer 1

由于arrays 是垂直居中，因此将两个 s 并排设置：

\documentclass{article}

\begin{document}

\[
  \setlength{\arraycolsep}{0pt}% Remove inter-column gap
  \renewcommand{\arraystretch}{1.2}% Space out equations
  \left\{\begin{array}{ r l }
    \sum F_x & {}= m \times a_n \\
    \sum F_y & {}= m \times a_t
  \end{array}\right.\kern-\nulldelimiterspace
  \quad\leftrightarrow\quad
  \left\{\begin{array}{ r l }
    T - m g \cos\theta & {}= m \times a_n \\
      - m g \sin\theta & {}= m \times a_t
  \end{array}\right.\kern-\nulldelimiterspace
\]

\end{document}

Answer 2

\documentclass[12pt]{article}
\usepackage{amsmath}
\begin{document}

\[
\begin{cases}
    \Sigma F_\mathrm{x} = m \times a_n \\
    \Sigma F_\mathrm{y} = m \times a_t
\end{cases}
\leftrightarrow \ \
\begin{cases}\!
    \begin{aligned}
        T - mg\cos\theta  &= m \times a_n \\
        {}- mg\sin\theta  &= m \times a_t
    \end{aligned}
\end{cases}
\]    

\[
\left\{\!
\begin{aligned}
    \Sigma F_\mathrm{x} &= m \times a_n \\
    \Sigma F_\mathrm{y} &= m \times a_t
\end{aligned}\right. \ \
\leftrightarrow \ \
\left\{\!
\begin{aligned}
    T - mg\cos\theta  &= m \times a_n \\
    {}- mg\sin\theta  &= m \times a_t
\end{aligned}\right.
\]

\end{document}