402.3B1 Open Sets in the Standard Metric Topology
What makes a subset of the real numbers an "open set" in the standard sense? Definition and a proof of the theorem that every finite open interval (a,b) is an open set. See the playlist: matthematics.com/real
0:00 Introduction and the "Horizon"
1:24 Motivation for Open Sets
2:15 Definition of Open Set, Three Ways
4:38 Open Intervals are Open Sets (Proof)
13:24 What Else Can There Be?
Пікірлер: 11
best instructor i have ever seen.i hope my exam will be okay. thanks a lot.
I swear you are the best instructor out there. I really appreciate your videos thank you a lot! I really wish if there are more videos on topology :(
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Thank you Dr ! Pls can you explain theorem of connectedness ?real numbers =AUB.? A and B nonempty subsets .
@MatthewSalomone
2 жыл бұрын
You might enjoy the end of this video where I “connect” that idea with clopen sets. kzread.info/dash/bejne/kZVrxq2QqMnSprA.html
Enjoyable video. 11:44 "a/2 is definitely greater than a"? that doesn't seem right. I'm sure you assumed the details could be filled out by the viewer. Here is my attempt at proving (a,b) is an open set, based on your video. Let x be arbitrarily given in (a,b) , and choose E = 1/2 min { x - a, b - x } . We will show that (x - E , x + E ) ⊆ (a,b). 1. x - E > x - ( x - a ) / 2 , since E - (x-a )/2 , and then add x to both sides (these are valid by field axioms/theorems). 2. x - ( x - a ) / 2 = x/2 + a/2 , by algebra simplification. 3. x/2 + a/2 > a/2 + a/2 , since we assumed x > a therefore 1/2 * x > 1/2 * a , or x/2 > a/2 . 4. a/2 + a/2 = a , by algebra simplification. By transitivity of inequalities, or putting the inequalities together, we get x - E > a. Similarly we can show x + E So far we have shown that a Let y be given in ( x - E , x + E ) . Then a Since y was given arbitrarily, we have for all y if y∈ (x - E , x + E ) then y ∈ (a,b). Therefore (x - E , x + E ) ⊆ (a,b) Since x in (a,b) was given arbitrarily, we get for all x in (a,b) there exists E such that (x - E , x + E ) ⊆ (a,b).
10:45 This is the picture of their vacation they post on Instagram despite the rest of their life is falling apart Oof, I did not need to be called out like that
@MatthewSalomone
2 жыл бұрын
Analysis proofs do be like that tho
Sir ! Have you made videos on Free Groups ?
Your representation is easy to understand, but your proof is incorrect when you prove x-epsilon>a and x+ epsilon>b.
@xoppa09
Жыл бұрын
correction: x+ epsilon also i think the proof is easier if you use ε = min { x-a, b -x }