# Problem with text position in math underbrace

I'm trying to write under a system of equation that it is impossible with the following code:

$\underbrace{\begin{cases} a = -1\\ b=2\\ (-1-4)-i(2+8)=-8i\implies -5 -10i = -8i \end{cases}_{\text{Sistema impossibile}}}\bigcup\begin{cases} a=0\\ b=2\\ -i(2^3)=-8i \end{cases}$


The problem is that the text gets positioned badly as you can see in the pic:

How can I get the text to actually be under the brace and not there? Thanks in advance for the answers.

• What would \bigcup mean? Do you perhaps mean \lor? Sep 25, 2020 at 21:28
• \bigcup gets the big union symbol(there is a second system which I haven't showed in the picture). What's \lor for? Sep 25, 2020 at 21:36
• You can contact the user egreg using directly the @ + name, because probably he not see your comment. Sep 25, 2020 at 21:41
• @user66094 \bigcup is meaningless in that context. Sep 25, 2020 at 21:54

An \underbrace positions its label the way the \sum operator gets its lower limit: entered as a subscript. In the code sample the subscript label comes right after \end{cases} instead of after the whole \underbrace{...} due to a misplaced close-brace character (so the intended label was an ordinary subscript for the cases environment). Moving the brace to come before the subscript fixes the trouble, as in this MWE.

\documentclass[12pt]{article}
\usepackage{amsmath,amssymb}

\begin{document}
$\underbrace{\begin{cases} a = -1\\ b=2\\ (-1-4)-i(2+8)=-8i\implies -5 -10i = -8i \end{cases}}_{\text{Sistema impossibile}}\bigcup \begin{cases} a=0\\ b=2\\ -i(2^3)=-8i \end{cases}$
\end{document}


Addendum with the \lor command as by comment of the user @egreg.

\documentclass[12pt]{article}
\usepackage{amsmath,amssymb}

\begin{document}
$\underbrace{\begin{cases} a = -1\\ b=2\\ (-1-4)-i(2+8)=-8i\implies -5 -10i = -8i \end{cases}}_{\text{Sistema impossibile}}\lor \begin{cases} a=0\\ b=2\\ -i(2^3)=-8i \end{cases}$
\end{document}


• Thank you, it worked Sep 25, 2020 at 21:32
• Just to point out what the problem & solution were: The question had a misplaced close-brace after \end{cases}, so \underbrace took both the cases environment plus the subscript as its first argument. Sep 25, 2020 at 23:36
• @DonaldArseneau Hi, can I help this favour, please? I'm not very good, often, to explain in English language the problem. If I use the translator I not know if the english motivation is correct or not correct. On your comment I am agree totally with you. At this moment I'm writing, for example, without the use of translator. (Before I think in Italian and after my mind translate in english :-( ). Can you edit adding your comment, please? Sep 26, 2020 at 10:50
• Oh, OK @Sebastiano. I also agree completely with your answer, but will add a few words -- in English :-) Sep 26, 2020 at 11:03
• @DonaldArseneau :-) welcome for your edit.....and thank you. At this moment my mind it is to school for my students: I'm using Google Suite, electronic papers for the exercises and now I'm in tilt. :-( GRazieeeeeeeeeeeeeeeeeeee. Sep 26, 2020 at 11:14