Hi @vaporeon_ I forgot to ask last night if you were familiar with the formulas

sin(x + y) = sin(x)cos(y) + cos(x)sin(y)
cos(x + y) = cos(x)cos(y) - sin(x)sin(y)
?

@wallhackio I have heard of these formulae before, but I do not remember how to prove this...

@vaporeon_

@vaporeon_ @wallhackio you people are smarter than me how do you pull proofs for random shit out of your ass

@cam @wallhackio Not "you people", only Clodsire, I am big stupid idiot who didn't know how to prove that formula

@vaporeon_ @wallhackio idk I stopped math at calculus and I hardly learned that. I didn’t even take linear algebra

@wallhackio @vaporeon_ or multivariate

@cam @wallhackio Multivariate is when you take derivatives or integrals of functions of more than one variable, right? I barely passed the exam, but I wouldn't say that I understand it properly (though I for sure could take a derivative of multiple variables if you asked me to). We had some complicated stuff in the last weeks, and at that point I had given up, and now I can't even remember what it was called

@cam @wallhackio I found the lecture PDFs on my hard drive (it's in German, so it won't help if I send it to Clodsire), so in case Clodsire wants to infodump on me about the topics that I forgot and/or never understood:

We did integrals on curves and then on surfaces and that's when I gave up, I don't think I can do an integral on a surface or even understand what's being asked of me

I also forgot what a divergence is and I had given up by the point that we covered whatever this is

@vaporeon_ @cam there's a great book called Div Grad Curl if this interests you and you would like a presentation that gives a good balance of formality and conceptual intuition