[Tex/LaTex] How to put big brackets under different parts of an equation to attach text labels


How do I put big brackets under different parts of an equation so that I can write, e.g., text specific to these parts?

For example:

f =  x^3 +  2
    |___|  |__| 
      |     |
   text 1  text 2

Best Answer

Since the text used in \underbrace (or \overbrace) is typically set in a different font size to not distract further from the equation, it is preferable to use amsmath's \text macro.

enter image description here

% \usepackage{amsmath}
\usepackage{mathtools}% Loads amsmath
  f(x) = 
    \underbrace{(x + 2)^3}_\text{text 1} + 
      \mathrlap{\overbrace{\phantom{(c - 2d)}}^{\text{text 2}}}
      (c - 
      \mathrlap{\underbrace{\phantom{2d) + (3e}}_{\text{text 3}}}
      2d) +
      \overbrace{(3e - 4f)}^{\text{text 4}}
    \bigr) + 
    \overbrace{(x - 3)}^\text{text 5}

The difficult overlapping braces uses math overlaps from mathtools. It follows a process of setting the \over-/\underbrace text first with a \phantom base, after which the base (or part thereof) is re-set. However, if those aren't needed, using amsmath only would suffice for usage of \text.

There are a number of ways of achieving the overlapping output. Another method of overlapping braces is discussed in section 63.2 Overlapping braces of the mathmode document.