If you haven’t heard about Khan Academy, let me be the first one to introduce you to its wonders. There is a huge library of 10-12 minute educational videos on high-school and college level topics from matrix math to trigonometry to how mortgages work. You need to read the background, it’s an unbelievably prolific individual guy, Kahn, who records each one of these. From what he says, he’s not an expert in all of them, he just ‘bones up’ on the topic and then records the session. The quality of the teaching is really amazing.
Case in point. A few weeks ago I had to recall how and why matrix multiplication works. I knew that stuff cold, 40 years ago. Yesterday I had to bone up on sines and cosines and the simple math there. I didn’t even remember that this stuff is called trigonometry (I was looking under geometry.) In each case I thought, oh I will just google it. I will look in wikipedia. I spent 15 minutes without success and then I went to Khan academy. Another 20-30 minutes later and I was up to date on the basic trigonometry and matrix knowledge that I needed.
Amazing. Check Khan Academy out.