Gfyuki

I am trying to achieve this look:

documentclass{article}

usepackage{amsmath}

begin{document}

        $dfrac{2x+7}{x-4}-dfrac{x+4}{x-2}$

end{document}

documentclass{article}

usepackage{amsmath}

usepackage{graphicx}



makeatletter

DeclareFontFamily{U}{tipa}{}

DeclareFontShape{U}{tipa}{m}{n}{<->tipa10}{}

newcommand{arc@char}{{usefont{U}{tipa}{m}{n}symbol{62}}}%



newcommand{arc}[1]{mathpalettearc@arc{#1}}



newcommand{arc@arc}[2]{%

    sbox0{$m@th#1#2$}%

    vbox{

        hbox{resizebox{wd0}{height}{arc@char}}

        nointerlineskip

        box0

    }%

}

makeatother



newcommand{stackAboveArc}[2]{begin{array}[b]{@{}c@{}}#1\ arc{#2}end{array}}



begin{document}

    %   $dfrac{2x+7}{x-4}-dfrac{x+4}{x-2}$

      $dfrac{stackAboveArc{x-2}{2x+7}}{x-4}-dfrac{stackAboveArc{x-4}{x+4}}{x-2}$

end{document}

I don't need any color or font different from the defaults.

EDIT:
Well I and modified something which is scaling with the fractions which is great but I can't rotate the arc. How to rotate it? Picture above.

Here is a proposal that marries your command with this answer by egreg.

documentclass{article}

usepackage{amsmath}

makeatletter% based on https://tex.stackexchange.com/a/260580/121799

newcommandunderparenonly[1]{%

  mathop{%

    vtop{

      m@th

      ialign{%

        ##crcr

        $hfildisplaystyle{#1}hfil$crcr

        noalign{kern3p@nointerlineskip}%

        upparenfillcrcr

      }%

    }%

  }

}

newcommandupparenfill{%

  $m@thsetboxz@hbox{$braceld$}%

  braceluleadersvrule @heighthtz@ @depthz@hfillbraceru$%

}

makeatother

newcommand{stackAboveChar}[2]{begin{array}[b]{@{}c@{}}underparenonly{#1}\[1ex]{#2}end{array}}

begin{document}

$stackAboveChar{x-2}{dfrac{2x+7}{x-4}}-stackAboveChar{x-4}{dfrac{x+4}{x-2}}$

end{document}

As for the code in your question: as you are already using graphicx, you could just add a rotatebox to flip the parenthesis.

documentclass{article}

usepackage{amsmath}

usepackage{graphicx}



makeatletter

DeclareFontFamily{U}{tipa}{}

DeclareFontShape{U}{tipa}{m}{n}{<->tipa10}{}

newcommand{arc@char}{{usefont{U}{tipa}{m}{n}symbol{62}}}%



newcommand{arc}[1]{mathpalettearc@arc{#1}}



newcommand{arc@arc}[2]{%

    sbox0{$m@th#1#2$}%

    vbox{

       hbox{resizebox{wd0}{height}{rotatebox[origin=bottom]{180}{arc@char}}}

        nointerlineskip

        box0

    }%

}

makeatother



newcommand{stackAboveArc}[2]{begin{array}[b]{@{}c@{}}#1\ arc{#2}end{array}}



begin{document}

    %   $dfrac{2x+7}{x-4}-dfrac{x+4}{x-2}$

      $dfrac{stackAboveArc{x-2}{2x+7}}{x-4}-dfrac{stackAboveArc{x-4}{x+4}}{x-2}$

end{document}