Question Number 159736 by LEKOUMA last updated on 20/Nov/21
$${Prove}\:{that} \\ $$$$\left.\mathrm{1}\right){Sup}\left({A}\cup{B}\right)={ma}\mathrm{x}\left(\mathrm{S}{up}\left({A}\right),\:{Sup}\left({B}\right)\right) \\ $$$$\left.\mathrm{2}\right)\:{inf}\left({A}\cup{B}\right)={min}\left({inf}\left({A}\right),\:{inf}\left({B}\right)\right) \\ $$