It’s about the quickest and most concise illustration I can offer of Guershon Harel’s necessity principle. The moment of need is brief, but really hard to miss. It sounds a lot like laughter.

2014 Feb 19. Christine Lenghaus adapts the interaction for naming angles:

I drew a large triangle and then lots of various sized ones inside it and asked the students to pick an acute angle. I asked a student to describe the one they were thinking about and then another student to come up and mark it! This lead to discussion on how best to label so that we both agree on which angle we were talking about. Gold!

Featured Comment

Joel Patterson:

There’s an easy way to do this in Geogebra.
Open up blank Geogebra file, viewing only the Geometry window (no Algebra window).

Click the point tool and make a bunch of points like in Dan’s video.

Then there is a small button AA with one A in black and the other in grey. This button shows and hides labels for all points.

Featured Tweets

@ddmeyer @JustinAion @TracyZager awesome. Basic premise to lesson design: What happens if we *don't* have definition/concept/skill X?

— Casey Rutherford (@rutherfordcasey) August 29, 2014

@fawnpnguyen @JustinAion @ddmeyer @TracyZager Yes, this. Naming points wasn't boring for folks that came up with it, I expect. We made it so

— Casey Rutherford (@rutherfordcasey) August 29, 2014

Featured Academic

Hans Freudenthal:

Youngsters need not repeat the history of mankind but they should not be expected either to start at the very point where the preceding generation stopped.

2017 Oct 16. Here are the slides.