And immediately preceding that equation is this sentence: "If it sounds simple, it is not, but if you’re interested it’s a great reason to learn spherical harm

And immediately preceding that equation is this sentence: "If it sounds simple, it is not, but if you’re interested it’s a great reason to learn spherical harmonics." The entire point of showing off that equation is to say "This stuff is actually really deep and complicated and it's a rich subject to dive into on its own if you want to go for that, but I'm not going that route."