Prove that the set (-2, ∞) is unbounded above and has no minimum element.

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- May 20th 2013, 09:07 AMAW63Proving that a set is unbounded above
Prove that the set (-2, ∞) is unbounded above and has no minimum element.

Help please (Worried) - May 20th 2013, 09:24 AMPlatoRe: Proving that a set is unbounded above
- May 20th 2013, 09:58 AMHallsofIvyRe: Proving that a set is unbounded above
S has no upper bound

Proof by contradiction: Suppose S has an upperbound, a. Certainly, 0 is in S so we must have 0< a. Then a< a+ 1 so a+ 1 is not in S. But S contains all numbers larger than -2 so that is a contradiction

S has no smallest member.

Proof by contradicton: Suppose S has smallest member b. Since b is in S, -2< b. Now, -2< (b- 2)/2< b is larger than -2 so in S but less than b which contradicts the assumption that b is the smallest member of S.