documentclass{article}
usepackage{amsmath}
egin{document}
egin{equation}
D_{it} =
egin{cases}
1 & ext{if bank $i$ issues ABs at time $t$}
2 & ext{if bank $i$ issues CBs at time $t$}
0 & ext{otherwise}
end{cases}
end{equation}
end{document}
left(
usepackage{amsmath}
underbrace{(x + 2)^3}_ ext{text 1}