documentclass{ctexart}
usepackage{amsmath}
usepackage{tikz}
usetikzlibrary{decorations.pathreplacing}
ewcommand ikzmark[2][0,0]{%
ikz[baseline,remember picture,overlay]
coordinate (#2) at (#1);}
egin{document}
$k$个$k$个$k$个$k$个$k$个$k$个$k$个$k$个$k$个$k$个$k$个$k$个$k$个$k$个$k$个$k$个$k$个$k$个$k$个$k$个$k$个$k$个$k$个
[
A_{km}(x)=2^{
ikzmark[0pt,4.5pt]{C1}
2^{2^{cdot^{cdot^{cdot^{
ikzmark[2pt,4pt]{C2}
2^{x^{
ikzmark[0pt,3.5pt]{C3}
2^{2^{cdot^{cdot^{cdot^{
ikzmark[2pt,4pt]{C4}
2}}}}}}}}}}}}},
B_k(y)=4^{
ikzmark[0.5pt,4pt]{B1}
4^{4^{cdot^{cdot^{cdot^{
ikzmark[2pt,4pt]{B2}
4^y}}}}}}.
%
ikz[remember picture,overlay]
{
draw[decorate,decoration=brace]
(C1)--node[shift={(135:8pt)}]{$scriptstyle k ext{个}$}(C2);
draw[decorate,decoration=brace]
(C3)--node[shift={(135:8pt)}]{$scriptstyle m ext{个}$}(C4);
draw[decorate,decoration=brace]
(B1)--node[shift={(135:8pt)}]{$scriptstyle k ext{个}$}(B2);
}
]
$k$个$k$个$k$个$k$个$k$个$k$个$k$个$k$个$k$个$k$个$k$个$k$个$k$个$k$个$k$个$k$个$k$个
end{document}