We love radians

Introducing trigonometry has become even more of a challenge than I thought. I think about each part of the lesson really hard; I want to give it a flow and focus on teaching the concepts. What I don’t want trigonometry to be is a huge mess of ad hoc rules.

Today was my introduction to radians. Looking back, my presentation was a bit more complicated than it needed to be to get the idea across. And what wasn’t clear (although that was one of my objectives) was why we use radians instead of degrees. So I’m going to start off class tomorrow with a little silent slideshow, replete with my own histrionics to make extraordinarily clear why we! love! radians!

Without further ado: why radians? (PDF file) [Unfortunately, SlideShare is only showing 18 of 23 pages for some reason. The PDF is complete.]

I’ve also come to realize that more is going on with kids than this whole forest for the trees crap that I wrote about before.

There’s a second reason things are getting mucked up, and that doesn’t have anything to do with my concept behind each lesson, or the flow, or anything like that. I realized today that a lot of the things that kids get tripped up on are (surprise surprise) basic facts about numbers. Is “1/2 times pi” the same thing as “pi over 2”? Yes. Do they know that? Possibly.

Or, for example, there’s the issue of manipulating visual and fractional information in their heads. We’re learning about radians, and we learn that there are “2 pi” radians in a circle. Then I ask them to draw an angle of “3 pi over 2” radians. It was as if I asked them to dance around like a chicken while singing Ave Maria. And since the “pi” was there, they thought that using the calculator wasn’t really going to help them.

I think we’re slowly getting it, but I’m not sure. I’m going slowly, but I have now started identifying key skills and concepts that need to be honed before we move on with radians. For example, because of what I noticed in my lesson on radians, we’re going to be practicing working with fractions (the eternal scourge of math teachers) and pi. (See my thrown-together worksheet here.)

Imagine (for surely, gentle reader, this has never happened to you before) that you’re at a mini golf course and you’re putting at the infamous and dreaded windmill hole. By mandate from the PuttPutt gods, you are not allowed to leave until you get the ball into the windmill. There’s a mini golf coach there, trying to give you advice and show you how to hold the club and how to swing. However, after 20 tries you aren’t getting it. And then you try another 2o times. No luck. Now tell me how you think you’d feel at your mini golf coach who has been standing there trying to help you.

There will be whining, complaining, anger, and frustration — anxiety — all directed to this coach.

The analogy isn’t quite right, and I hope that my students don’t direct those feelings to me (this was an extended allegory, duh), but I can’t help but notice that the anxiety level has shot up in my room in the past two weeks, when I feel that one of my teaching talents is keeping a totally relaxed atmosphere.

UPDATE: My presentation (see above) on”Why Radians?” took 5 minutes and I think did the trick. I did it in both classes, and both seemed to get it. And the levity of it all made the classroom less tense. And with Spring Break descending upon us, we’re going to have a much needed break.



  1. It’s days like this where I want big painted concentric circles on the PE asphalt outside my room. (A number line would be nice too). A full day project with table & calculators and those rolling measurement thingies you see surveyors use these days would be a great kinesthetic intro to how fractions of a circle translate to the same ratio between radius & partial perimeter.

    maybe i’ll do that for pi day tomorrow.

  2. Theres a really nice teaching and learning plan about radians on the home page of project maths (A maths initiave in Ireland). I think you might find it very interesting. Have a look at http://www.projectmaths.ie and look for the “Radians” teaching and learning plan on the front page.



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