\implies 来自上面的行

Question

在如下所示的多线方程中，表示“从上面一行可知……”的正确数学符号是什么？

\documentclass[12pt,oneside]{article}
\usepackage{libertine}
\usepackage{amsthm}
\usepackage[libertine]{newtxmath}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage{mathtools}


\begin{document}
\begin{align*}
    \overline{x} = \frac{4(1+r+r^2)}{3\pi(1+r)} &= r\\
    4(1+r+r^2) &= 3r\pi(1+r)
\end{align*}
\end{document}

或者只是将其放置\implies在每行的开头？

Answer 1

也许您正在寻找\ArrowBetweenLinesfrom mathtools。就我个人而言，我更喜欢简单的\shortintertext：

\documentclass[12pt,oneside]{article}
\usepackage{libertine}
\usepackage{amsthm}
\usepackage[libertine]{newtxmath}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage{mathtools}


\begin{document}
\begin{alignat*}{2}
                                 & & \overline{x} = \frac{4(1+r+r²)}{3π(1+r)} & = r \\
  \ArrowBetweenLines[\Downarrow] & & 4(1+r+r²) & = 3rπ(1+r)
\end{alignat*}
\begin{alignat*}{2}
  \overline{x} = \frac{4(1+r+r²)}{3π(1+r)} & = r & & \\
  \ArrowBetweenLines*[\Downarrow]4(1+r+r²) & = 3rπ(1+r) & &
\end{alignat*}
\begin{align*}
  \overline{x} = \frac{4(1+r+r²)}{3π(1+r)} & = r \\
  \shortintertext{whence}
  (1+r+r²) & = 3rπ(1+r)
\end{align*}

\end{document}