Linkfest for Saturday, April 5

• This video shows multiplying by using a parabola. Completely impractical, but I was curious why it worked. I figured it out and then wondered if my pre-calculus students could figure it out too. I wanted a demo instead of a video, so I built something in Desmos. (Hide the equations, and click on the three dots. The middle dot will always multiply the absolute values of the other two.) It's not perfect, but it might be good enough to impress my students.
• I've seen this cute list of functions, with the person's arms illustrating the graph, on a number of blogs lately. I see two that are wrong. Henri sees one wrong, and has quibbles with four of them. What do you see?
• Common Core for math... I keep hearing that the math standards are pretty good. But if the tests ignore the most important standards (the process standards, which describe mathematical thinking), then they're being used badly. This post by Jonathan Katz goes into some detail.
• Nice exercise. One person looks at the board, and describes the graph drawn there. Their partner must draw it from the verbal description.
• Quintic polynomials. There is no formula for the roots. But there is this. I want to learn more!
• Fawn's lesson for proportional thinking.
• Papert on "hard fun."
• I like this diagonal problem, but when I tried it in class my students were not persistent enough to succeed with it. David Cox's post on how he used it with his students makes me want to try it again.
• In whatif?, xkcd's creator, Randall Munroe, takes a silly question and analyzes it with math and physics to come up with an answer. In this episode, he figure how how big a splash you'd get from a tree as big as all trees on earth falling into an ocean with the water of all the ocean's on earth.
• In this post from her calculus for kids series, I like Maria's thoughts on how we help kids learn problem-solving.