## Thursday, November 15, 2012

### What's the best way to clean up blown minds? With more awesomeness!

Similarity is a tricky topic; somehow it always ends up being more challenging to teach every year that I teach it. I think I learn something new every time that I hit this topic in geometry, which perplexes me because its a rather simple concept. Two figures, same shape, different sizes: done. Sure, when I start talking about the ratios between similar figures' areas/volumes, things start to get interesting, but overall, not a difficult idea to wrap my mind around. I feel like my students always have this approach as well. They find out we're going to be discussing similar figures and they get excited because we're going into an 'easy' topic, but by the end they always leave thinking, "Woah. That was intense." Perhaps I should stop telling them on the first day, "Hey guys good news. We're talking about similarity, one of the easiest topics in the course." Yeah, I probably set them up a little bit.
This year's enlightenment came unexpectedly when I placed a seemingly easy warm-up problem on the board yesterday. We've pretty much discussed similarity in as much detail as possible, so my students' brains are fairly swollen from the amount of knowledge they've gained up until this point (more on that in a second). The problem looked like this:

"My classroom is about 30ft long and takes up about 700 sq ft. If I want to draw it to scale so that it has a length of 5in, how much space on my paper do I need to reserve for my classroom?"

No problem, right? Calculate your scale factor, square it, use that to calculate your new, smaller area. Done and done. I figured we'd be able to answer this question plus the three others I had on the board within 10 minutes tops. Right? Sounds reasonable? I mean, it is just a simple problem, nothing new. We've been talking about these relationships for the last two or three days. Welp, as it turns out, I'm bad at predicting these kind of things.
Here is brief visual as to what ensued (if only my whiteboard could've captured everything that was said. Unfortunately I had to erase some awesome ideas because I was running out of room):

(I apologize for my poor panoramic cut, slice, paste job)

This single problem generated more discussion than anything we've discussed all semester. My whole 10 minute idea went out the window, we spend ONE HOUR talking about this problem. Now, I'm not upset by this. I believe there are many teachers out there who at this point in the blog would begin writing about how annoyed they were that they had to reteach topics and what not. I had quite the opposite experience; this was one of the best hours of my teaching career! I had 10 different students show 10 different ways on how to solve this thing. It was ridonkulous (that's right, I went there).