Ooh, definitely a possibility, if I add a couple rays. Thanks!

Eh, depends on whether there's another step after? x^2=9, |x|=3, I'd teach both as +-3. But given x-h in either, the "split" seems necessary.

These are adorable!

Ooh, I love the bit about independence - my students have a hard time with that too! (Oddly, not during probability unit, but in chi-square testing, hoo boy.)

It only ever made sense to me in certain contexts. Like product needs and sales over the week. Ok, if A takes a&b&c to make and I expect to need x&y&z on M,T,W, and I also have products BCD, how much a,b,c should I order; that's a linear of Ax+By+Cz, ok. I also do the shifted up 2nd matrix layout.

Spelling was only just starting to standardize then and wouldn't get to modern notions of 'standard' until the 1800s. I am surprised to see it in sine, though; I had the impression Latin/Greek borrowings, especially for math/sci, drifted less.