如何将两个方程组并列放置？

Question

标题说明了一切。我试过了

\begin{alignat*}
& \begin{aligned} & \begin{cases}
m \Ddot{x} = m g \cdot sen(\theta) - F_r \\
    m \Ddot{y} = m g \cdot cos(\theta) - N = 0 \\
    I \Ddot{\phi} = \sum \tau = \Vec{R} \times \Vec{F_r}
  \end{cases}\\
  \MoveEqDown
  \end{aligned}
    \Rightarrow
  \begin{aligned}
  & \begin{cases}
  \vspace{1mm}
  m \Ddot{x} = m g \cdot sen(\theta) - \mu \cdot m  g \cdot cos(\theta) \\
    m \Ddot{y} = m g \cdot cos(\theta) - N = 0 \\
    I \Ddot{\phi} = R \cdot \mu \cdot mg \cdot cos(\theta) \cdot sen(\alpha)
  \end{cases} \\
  \MoveEqLeft[-1]
  \end{aligned}
\end{alignat*}

它显示的内容与发布的图片类似。那个箭头太烦人了，一定有更简单的方法吗？

Answer 1

这是您想要实现的吗？您必须嵌套aligned，cases而不是相反。外层alignat是不必要的。

\documentclass{article}

\usepackage{mathtools}

\begin{document}

    \[ \begin{cases}
       \begin{aligned}
m \Ddot{x} & = m g \cdot \sin(\theta) - F_r, \\
    m \Ddot{y} & = m g \cdot \cos(\theta) - N = 0, \\
    I \Ddot{\phi} & = \sum \tau = \vec{R} \times \Vec{F_r}
  \end{aligned}
  \end{cases}
    \implies\enspace
  \begin{cases}
  \begin{aligned}
   m \Ddot{x} & = m g \cdot \sin(\theta) - \mu \cdot m g \cdot \cos(\theta), \\
    m \Ddot{y} & = m g \cdot \cos(\theta) - N = 0, \\
    I \Ddot{\phi} & = R \cdot \mu \cdot mg \cdot \cos(\theta) \cdot \sin(\alpha)
  \end{aligned}
  \end{cases} \]%

\end{document}