Matrix math, where have you been all my life?

Because I want to for reals understand how machine learning works, I'm relearning calculus, plus a few pre-calc subjects I somehow missed the first time around.

I have three observations:

There really is an amazing amount of instructional material just sitting there on the internet for anyone to use for free.
A lot of it is really badly presented. (I'm getting by with mostly Khan Academy content, but it's a bit disorganized and very oriented around teaching-to-the-test instead of here's-why-this-matters. If anyone has better suggestions I'd love to hear!)
Software developers and mathematicians approach the same problems completely differently, and the mutual incomprehension when they try to explain things to one another is pretty amazing to watch. I suspect there are a lot of easy discoveries and inventions to be found if those groups could come up with a common language....