[Tex/LaTex] Underbrace problem

Question

I have some problem to make the Underbrace partly for the equation like the picture shows. The unique part is the "b" is used twice.

Thanks !

Answer 1

You can underbrace “a+(nothing)”, print a zero width “b” and again underbrace “(nothing)+c”:

\documentclass{article}
\usepackage{mathtools}
\begin{document}
\[
\overbrace{
  \underbrace{a+{}}_\text{text}
  \mathclap{b}
  \underbrace{{}+c}_\text{text}
}^{\text{text}}
\]
\end{document}