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

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. If you enjoyed this video please consider liking, sharing, and subscribing. You can also help support my channel by becoming a member    / @themathsorcerer   Thank you:)