Happy to see someone else who watches Michael Penn videos.
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YouTube has become a fantastic place for this long tail of content, in this particular case a bunch of interesting math problems and tricks presented on a blackboard. Or, even full classes, from a person focused on honing pedagogy.
3blue1brown is another amazing channel for math as well.
I have a feeling that this sort of content is the seeds of very great things for humanity. In the 20th century, ET Jaynes talks about how people never get credit in academia for creating simpler paths to greater understanding. But with YouTube, creators can both reach an audience and also find patrons to support them, or maybe even make a living off of YouTube directly with enough viewers.
Motivated students have such resources at their fingertips just from an internet connection, if they happen to get lucky enough to find the right resources.