Video for Class

I'm have to go to a training session at school tomorrow, which means I'll be missing one period of the day. Today's a snow day, so we're already missing a day this week. We have lots to get done in class and I don't want to waste tomorrow. So I had the genius idea (!) of making a video for them. But then I had to figure out how to produce it. I thought of using screen-cast-o-matic - that thing is amazing. It's like a screenshot, but it does videos. However, for my video I have to write math stuff and draw triangles, which isn't so easy with a trackpad or even a mouse. So no scree-cast-o-matic. Instead, here's what I came up with. I feel so low tech.