Question Number 103180 by mohammad17 last updated on 13/Jul/20
$${Let}\:{S}\:{be}\:{a}\:{nonempty}\:{subset}\:{of}\:{R}\:{that}\:{is}\:{bounded} \\ $$$${below}\:.\:{prove}\:{that}\:\left({inf}\left({S}\right)=−{sup}\left\{−{s}:{s}\in{S}\right\}\right)? \\ $$