The live in class videos of yours are way more interesting and involving, it feels like I am in the class. In general, all of your videos are great though!
I know this is late so I’m commenting for those who have the same question. P(x) or R ( radius ) as others call it, varies. Since it varies it’s represented as X. Sometimes axis of rotation is farther away so it’s p(x)= #-x. Hope this helps those in the future. He explains it at 12:00
