Ajot
- 2
- 0
Show that a set of real numbers E is bounded if and only if there is a positive number r so that |x| <r for all x \epsilon E.
My Attempt:
This is what I have done, and not sure if I am on the right path. Math proofs are pretty difficult for me so please any help would be greatly appreciated.
I knew I had to show both ways of the proof due to the "if and only if"
1. s => r
Set of real numbers E is bounded => a positive number r so that |x| < r for all x \epsilonE.
\exists bounded set E
Assume E: {0 < x < 1} (or { 0 \leq x \leq 1} wasn't sure which one to use)
By the Completeness Axiom, E has a least upper bound
1 is the least upperbound
1 > 0
r= 1
|x| < r
r is the least upper bound and E is bounded
2. r => s
a positive number r so that |x|< r for all x\epsilon E. => set of real numbers E is bounded
\exists r (r > 0)
Let there be a unbounded set of reals E
\exists x (x \epsilon[\tex] E)<br /> |x| < r (given) therefore by definition of upper bound, r is an upper bound<br /> therefore E is not a unbounded set of reals<br /> E is a bounded set of reals<br /> <br /> <br /> I feel like there are a lot of holes and I just want to be able to improve my math proofing skills. Thanks for the help.<br /> <br /> =)