A few weeks ago, a classmate from gradskool posted a link on Facebook to a site with a number of GIFs that illustrate mathematical principles underlying many concepts from geometry, trigonometry, and calculus.
I thought the constructs on the page were fascinating. Some required quite a bit of concentration, and with some I really had to dredge up hazy memories from my math courses even to get a rough idea what they were talking about.
The GIFs are fun to study, but I really don't think they necessarily do a better job of teaching the concepts than my various instructors did. Here's one that made a lot of sense once I looked at it for a minute. It really might have helped me in high school math.
If you’re studying trig, you better get pretty comfortable with circles. Check out this visualization that shows what you’re really looking at when you deal with pi:
You might enjoy the others, too.