How to change these formulas?

Question

I would like to modify 2 of formulas like the figure below. Could you help me?

\documentclass[a4paper,12pt]{article}[12pt] 
\usepackage[italian]{babel} 
\usepackage[T1]{fontenc} 
\usepackage[utf8]{inputenc} 
\usepackage{anysize}
\usepackage{graphicx}
\usepackage{amsmath}
\usepackage{amssymb}
\usepackage{mathrsfs} 
\usepackage{textcomp} 
\linespread{1.5}

\frenchspacing 

\newcommand{\abs}[1]{\lvert#1\rvert}

\usepackage{floatflt,epsfig}

\usepackage{multicol}




  \usepackage[a4paper,top=1.0cm,bottom=1.0cm,left=1.0cm,right=1.0cm]{geometry}


\begin{document}


$ a^2 = 16 \rightarrow a = \pm 4 =  $

\newpage

$ x \cdot \left( x+3\right)  = 0 \rightarrow $




\end{document}

Answer 1

Here is how to do it with pstricks and mathtools (for the \underbracket command).

Unrelated: the epsfighas been obsolete for more than 20 years, and should be replaced with graphicx. Also, since version 3.10 the language options of babel should be loaded with the document class, so language-dependent packages be aware of the language of the document.

\documentclass[a4paper,12pt, italian, svgnames]{article}[12pt]
\usepackage{babel}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage{anysize}
\usepackage{graphicx}
\usepackage{amssymb}
\usepackage{mathrsfs}
\usepackage{textcomp}

\usepackage{mathtools}
\usepackage{pst-node}
\usepackage{auto-pst-pdf} %% to compile with pdflatex --enable-write18 (MiKTeX) or pdflatex --shell-escape (TeX Live, MacTeX))
\newcommand\mathpnode[1]{\pnode[0,\fontdimen22\textfont2]{#1}}

\linespread{1.5}

\frenchspacing
\DeclarePairedDelimiter{\abs}{\lvert}{\rvert}

\usepackage{floatflt}%
\usepackage{multicol}

 \usepackage[a4paper, margin=1.0cm]{geometry}

\begin{document}

\begin{pspicture}
$ a^2 = 16 \rightarrow a = \pm 4 = \mathpnode{M}\qquad\begin{aligned}
  \mathpnode{R1} & \mathbf{ + 4} \\[1ex]
  \mathpnode{R2} & \mathbf{ - 4}
\psset{nodesep = 3pt}
\ncline{M}{R1}
\ncline{M}{R2}
\end{aligned} $
\end{pspicture}
\bigskip

$\psset{fillstyle = solid} \underbracket[0.8pt]{\,x\vphantom{)}\,}_{{\substack{\vert\\\pscirclebox[fillcolor = BlanchedAlmond]{1}}}}\! \cdot \underbracket[1pt]{( x+3) }_{\substack{\vert\\\pscirclebox[fillcolor = Aqua!40]{2}}}= 0 \rightarrow \quad\begin{aligned}
 & \raisebox{-0.3\height}{\pscirclebox[fillcolor = BlanchedAlmond]{1}}\quad\mathbf{x = 0}
\\[1ex]
 & \raisebox{-0.3\height}{\pscirclebox[fillcolor = Aqua!40]{2}}\quad\mathbf{x + 3\rightarrow x = -3}
\end{aligned}$

\end{document}