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The value in good mathematical books is mostly the exercises. Like Spivak, Rudin and Pugh. Struggling through those is vastly more valuable than any video or hand holding. I mean most of those problems would take hours or even days to solve. I suppose Khan videos (or at least the ones I’ve watched) are useful but it’s no substitute for active thought. What I like about videos from a real course is that you can “see” how a real mathematician thinks about attacking a problem.