Oversized \underbrace's label causes unwanted spacing

Question

Consider this:

\left( x-1 \right) \underbrace{ \left( ? \right) }_{ \text{what is this?} }

The label is longer than the braced portion, which causes unwanted space between the parentheses.

Is there a way around that, so that the parentheses "touch" as they would normally?

Please note that I just started on LaTeX, and I'm using TexMaths inside LibreOffice Writer.

Answer 1

The mathtools package (which loads and extends the amsmath package) provides the command \mathclap

If you decided to change the justification, you could use \mathllap

or \mathrlap

MWE

\documentclass{article}

\usepackage{mathtools}

\begin{document}

\[
    \left( x-1 \right) \underbrace{ \left( ? \right) }_{ \mathclap{\text{what is this?}} }
\]

\end{document}

Answer 2

You can place the content "what is this?" in a box of smaller width in order to remove this spacing problem:

\documentclass{article}
\usepackage{amsmath}% http://ctan.org/pkg/amsmath
\begin{document}
\[
  \left( x-1 \right) \underbrace{ \left( ? \right) }_{\text{\makebox[0pt]{what is this?} }}
\]
\end{document}​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​

In the above example, "what is this?" is placed in a zero-width box. You can modify this to suit your needs. For example, in this instance, since there's nothing else in the expression, it's fine. However, with other elements it may be required to have some space around "what is this?". Then some negative whitespace (or skipping) might also be useful.