I was wondering how I could lower the line below the underline in this image?
Here's the code I have so far :
\documentclass{article}
\usepackage[utf8]{inputenc}
\usepackage{amsmath,amsthm,amssymb,latexsym,amsfonts}
\usepackage{mathtools}
\usepackage{physics} % partial derivatives
\usepackage{tikz}
\usetikzlibrary{intersections, decorations.pathreplacing,shapes,shapes.geometric,hobby,patterns,babel,matrix,calc,snakes,backgrounds,shapes.multipart,shadows.blur}
\newcommand{\tikznode}[2]{% from https://tex.stackexchange.com/a/402466/121799
\ifmmode%
\tikz[remember picture,baseline=(#1.base),inner sep=0pt] \node (#1) {$#2$};%
\else
\tikz[remember picture,baseline=(#1.base),inner sep=0pt] \node (#1) {#2};%
\fi}
\begin{document}
Soit $A$ une matrice $\triangle$ supérieure (voir exercice pour : inférieure). Les valeurs propres de $A$ sont les racines de $p_{A}(\lambda)$ : \\ \\
$\begin{aligned}[t]
\det(A - \lambda I) &= \mqty|a_{1\,1} - \lambda & a_{1\,2} & & & \\ & a_{2\,2} - \lambda & a_{2\,3} & & \\ & & a_{3\,3} - \lambda & & \\ & & & \ddots & a_{n-1\,n} \\ & & & & a_{n\,n} - \lambda| \\
&\tikznode{detAI}=\, \underline{(a_{1\,1} - \lambda)(a_{2\,2}\tikznode{detAI1} - \lambda)\ldots(a_{n\,n} - \lambda)} \\
\\ \\ \\
\end{aligned}$
\begin{tikzpicture}[overlay,remember picture]
\draw[<-] (detAI.south) to[out=270,in=0]
($(detAI)+(-.46cm,-.65)$) node[below] {\scriptsize{\begin{tabular}{l}Le déterminant d'une \\ $\triangle$ supérieure est le produit \\ de ses éléments diagonaux.\end{tabular}}};
\draw[->] (detAI1.south) to[out=270,in=90]
($(detAI1)+(1.25cm,-1.45)$) node[below] {\scriptsize{$\underline{\lambda = a_{1\,1},\, a_{2\,2},\, \ldots,\, a_{n\,n}}$}};
\node[] at (7.15,1) {ne s'annule qu'en};
\end{tikzpicture}
\end{document}`
