Intro Real Analysis, Lec 31: Open Sets on the Real Line, Continuity & Preimages of Open Intervals

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Introduction to Real Analysis Lecture 31. Topology Unit, Part 1.

(0:00) Comments about content and the final exam.
(2:01) Today will be topology of the real line. The last two weeks we will use a more abstract approach involving metric spaces as well and apply the ideas to studying recursively defined sequences.
(3:13) An important property of open intervals (given any point in an open interval, there is an open interval centered at the point that is entirely contained in the given open interval) and give proof.
(14:07) Extend the property to unions of open intervals and give proof.
(22:47) Extend the property to the intersection of a finite number of open intervals and give proof.
(33:40) Definition of an open set (in the set of real numbers).
(36:13) Mention that any nonempty open set (in R) is the union of open intervals. Any such set can even be proved to be the union of a countable collection of disjoint open intervals.
(39:18) Theorem: Given a real-valued function defined on R, the function is continuous on R if and only if the preimage of any open interval is an open set.
(44:40) Sketch of proof.

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I am studying for a master's degree in applied mathematics and I had a lot of trouble understanding these topics. Thank you very much for your video. I have finally understood this topic. You are very good at explaining. Greetings from Mexico.

nemachtianimx
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Thanks so much for making these lectures publicly available. I'm passing my Intro to Real Analysis thanks to your help!! :)

richardvazquez
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Applied Math Major here, and also has MS in Stats. I would love to sit in your class. I love how you teach Topology with drawings.

yaweli
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Thank you very much! I am learning Real analysis and find open set hard to understand. Your video is very helpful!

bowlofsoba
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Cheers from South Africa, I’m writing final year exam for real analysis. Uniform continuity would be the next lecture I’d like to see Prof. Great upload🔥

damianboone
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Thank you so much sir. Your explanation is very lucid.

abhishekpaul
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At 9:07, isnt r <= b-x and r <= x-a since its the minimum. Example r= min(2, 3). so r = 2. so r <= 2 and r <= 3.

algorithmo
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I just wanted to say your lectures are unbelievably helpful! It has really been how I've understood my course. Out of curiosity, what book are you teaching from?

lanefarrel
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Which year of university is this lecture taught

algorithmo
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Sir, is there any chance you can upload linear algebra and topology lectures?

ritesharora