How to Prove that the Interval (a, b] is Not an Open Set

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In this video I will show you how to prove that the interval (a, b] is not an open set. I do a proof by contradiction and I go over all of the steps very carefully. I hope this video helps someone.

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Was just literally studying about this exact definition for multivariable analysis. Amazing how you always upload stuff I'm working on

liftsu
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Real analysis 1 brought me here and man am I so grateful for your videos. This stuff CAN be simple so long as its explained well! Thanks for doin what you do I am almost certain you have saved many a mathematics student's grade!

nullbrain
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Perfect timing, my upcoming test has this topic

BrettWoodPiano
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I like the way you make calculus seem easy

thierrry.k
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Thank you, I have a midterm tm and this has helped so much. Thank YOU!

MiguelMoreno-qcip
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thanks for this vid. i always have hard time proving these kind of obv. stuff. would love more analysis content.

turokg
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Learned a new symbol ( c with line below it ) thx

__.__-_.
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Who said mathematicians can't be cool😁 Thanks for the video

kunalbarua
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does not open imply closed or do you have to prove closedness separately?

pawpatrol
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I am trying to figure out why it is necessary to go to the trouble of bringing ε/2 into the argument rather than just using ε. The only difference appears to be the assertion that b+ε/2 is an element of (b-ε, b+ε)⊆ (a, b] and therefore b+ε/2 is an element of (a, b] and therefore b+ε/2 is <= b. The implication that I can not reconcile is that somehow (b-ε, b+ε) ⊆ (a, b] does not imply b+ε is an element of (a, b], for if it did it would not be necessary to use ε/2, as we could simply use ε to directly contradict in similar manner to ε/2. So what is the key realization that necessitates use of ε/2 ? My mind remains troubled by thinking it valid that (b-ε, b+ε) ⊆ (a, b] implies b+ε is an element of (a, b] and therefore b+ε is <= b setting up a more direct contradiction.

dvashunz
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Is there a video like this, showing that the set is neither closed?

MrCentrax
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YES! topology and ... we get to stay home because of corona. What better to do than study math.

maxpercer
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I sense a little bit of snark in the proof of contradiction LOL XD

yiuminghuynh
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How to prove that set of rational numbers is not closed??

masoomparwej