documentclass{article}
usepackage{tikz}
usetikzlibrary{fit}

newcommand{tikzmark}[2]{tikz[overlay,remember picture,baseline=(#1.base)] node (#1) {#2};}

begin{document}
[
 left[begin{array}{*3{c}}
    tikzmark{left_end}{0} & 2 & tikzmark{right_end}{1}\
    3 & -1 & 2 \
    tikzmark{down_left}{4} & 0 & tikzmark{down}{1}
  end{array}right]
]
tikz[overlay,remember picture] {
draw[red,thick,dashed] (left_end) circle (0.2cm);
    draw[-,red,thick] (left_end) -- ++ (1.5,0) (right_end);
    draw[-,red,thick] (left_end) -- ++ (0,-1) (down_left);
}
end{document}