答案1
以下是我手头方程式的排版方式——与您发布的屏幕截图并不完全相同。我不会为由此产生的差异辩解。
\documentclass{article}
\usepackage{newtxtext,newtxmath} % optional
\usepackage{booktabs} % for '\midrule' macro
\usepackage{array} % for '\newcolumntype' macroi
\newcolumntype{C}{>{{}}c<{{}}} % col. type for binary and relational symbols
\newcommand\mr[1]{\multicolumn{3}{r}{#1}} % handy shortcut macro
\begin{document}
Subtracting equation (3) from equation (4), we have
\[
\setlength\arraycolsep{0pt}
\begin{array}{lrCrCrCl}
& 5(2-i)z &+& 10iw &=& -5 &+& 5i\\
(-)\mkern18mu & 5(2-i)z &-& (7-i)w &=& 13 &-& 9i\rlap{\,.}\\
\midrule
& \mr{10iw+(7-i)w} &=& -18 &+& 14i\\
\Rightarrow & \mr{(7+9i)w} &=& -18 &+& 14i
\end{array}
\]
\end{document}