Very pretty! I like the handwritten equations particularly.

I first learned this almost fifty years ago, in a book I got in a second hand shop for $0.25 when I was in high school. Now I can barely remember not knowing these things.

(It's funny that many of my university courses I remember like I took them last week, but a few like Differential Geometry I remember nothing about. Now I'm finding out which classes I really paid attention to.)