What did you learn from it?

None of my math books are as obtuse as it is. The equations are presented on their own without explanations. On that page alone they're using quite a bit of mathematical notation that I, at least, have never seen before and I suspect it's largely unnecessary.

What did I expect? I expected a book that explained the concepts in plain english as well as mathematically. I expected the authors to be mature enough not to heavily decorate every single equation with as much mathematical notation as possible. Sort of like how bad coders make their code hard to read. That's the vibe I'm getting from the book.