Our Geometry Support Site

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So, I’ve talked about Khan Academy before. They make instructional videos for students to watch and learn from.


I’ve talked about #flipclass before. In this model, the teacher makes videos for the students to watch and learn from.


I like the idea of students having instructional videos to watch and learn from. But, in both Khan Academy (and other related sites) as well as flipped classes, the students are recipients of the videos. We decided that we didn’t want them to simply be recipients. We decided that we wanted them to be producers of the resources, too. So, we decided to just let the students create the math help videos.

Here’s what they did: Today I unveil the @PennGeometry Beta for your review and feedback. Currently, there are videos created from one practice test about triangle similarity. We would like to expand and continually improve.


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All of the videos are designed, produced, and completed by our students. Some of my students were sensitive to the boring math video and tried to add their personality to the video. We would love some comments, “likes”, and constructive feedback. Please check it out. Eventually, we want to add our voices to the overall mathematics community to support those in need.

Check it out and let us know what you think. We look forward to hearing from you.

For your students’ sake: Don’t stop being a learner

Yesterday, we designed an Algebra II lesson using 3D modeling to derive the factored formula for difference of cubes. As we began to finish up, Sheila (@mrssheilaorr), the math teacher sitting beside me made a passing reference to being frustrated trying to prove the sum of cubes formula. Me, being a geometry teacher by trade decided to give it a try perhaps hoping to offer a fresh perspective. I mean, I was curious. It looked like this:

2014-02-20 13.26.00

On the surface, it didn’t seem unapproachable. I quickly became frustrated as well. Most frustrating was the mutual feeling that we were so stinkin’ close to cracking the missing piece. Finally, Luann, a math teaching veteran sat down beside us, commented on her consistently getting stuck in the same spot we were stuck and then, as the three of us talked about it, the final piece fell in and it all made sense (it’s always how you group the terms, isn’t it?)

Then this morning, it happened again. Writing a quiz for Calculus, I needed a related rates problem. Getting irritated with the lousy selection of choices online, I decided that I needed to try to create my own. And I wanted to go #3Act and after some preliminary brain storming with John Golden (@mathhombre) (Dan Meyer’s Taco Cart? Nah… rates of walkers not really related…) we found some potential in Ferris Wheel (also by Dan Meyer)! Between my curiosity and my morning got mathy in a hurry.

First I tried to design and solve the problem relating the rotational speed in Act 1 to the height of the red car. That process looked like this:

2014-02-21 20.32.42

Meanwhile Dr. Golden found a video of a double Ferris wheel, which was pretty awesome. Seemed a little it out of my league, so kept plucking away at my original goal.

It clearly wasn’t out of Dr. Golden’s league, as he took to Geogebra and did things I didn’t know Geogebra was capable of. (You’re going to want to check that out.)

So, what is the product of all of this curiosity and random math problem-solving? As I see it, these past 48 hours have done two things: Reminded me of what makes me curious and reminded me what it’s like to be a learner.

I have a feeling my students will be the beneficiaries of both of those products. There’s a certain amount of refreshment that comes from never being too far removed from the stuff that drew us to math in the first place. The problem you want to solve just because you want to see what the answer looks like.

And this curiosity, the pursuit, it feeds itself. In the process of exploring that which you set out to explore, you get a taste of something else that you didn’t know you would be curious about until it fell down in front of you. (For example, Geogebra… have no idea what that program is capable of, which is a shame because it is loaded on all my students’ school-issued laptops…)

And this process breeds enthusiasm. Enthusiasm that comes with us into our classrooms and it spreads. I’m not trying to be cheesy, but much has been said about math functionality in the modern economy, how essential it is in college-readiness and the like with few tangible results. Let’s remember that there are kids who are moved by enthusiasm, who will respond to joy, who will pay attention better simply because the teacher is excited about what they are teaching. It won’t get them all, but neither will trying to convince them of any of the stuff on this poster.

Now, who’s going to teach me how to use Geogebra?

The Anxiety of Open-Ended Lesson Planning

It’s been about three years since I started weaning myself (and my students) off textbook-dependent geometry lesson-planning and toward something better. I’ll admit the lesson planning is more time-consuming (especially at the beginning), but most of the time expenditures are one-time expenses. Once you find your favorite resources, you bookmark them and there they are.

As we pushed away from the textbook, I noticed two things: First, the course became more enjoyable for the students. This had a lot to do with the fact that the classwork took on a noticeably different feel. Like getting a new pair of shoes, the old calluses and weak spots aren’t being irritated (at least not as quickly). Out went the book definitions and “guided practice” problems and in came an exploration though an inductively-reasoned course with more open-ended problems (fewer of them) that seemed to reward students’ efforts more authentically than the constant stream of “1-23 (odds).”

The second thing that I noticed, though, was that I had less of a script already provided. The textbook takes a lot of the guesswork out of sequencing questions and content. When the textbook goes, all that opens up and it fundamentally changes lesson planning. The lesson becomes more of a performance. There’s an order. There’s info that you keep hidden and reveal only when the class is ready. Indeed, to evoke the imagery of Dan Meyer (@ddmeyer) it should follow a similar model to that of a play or movie.

But, see… here’s the thing about the “performance” of the lesson plan. The students have a role to play as well… and they haven’t read your script… and they outnumber you… and there is a ton of diversity among them. So, when you unleash your lesson plan upon them, you have a somewhat limited ability to control where they are going to take it.

Therein lies the anxiety.

If a student puts together a fantastic technique filled with wonderful logical reasoning that arrives at an incorrect answer, you have to handle that on the fly. It helps to be prepared for it and to anticipate it, but the first time you run a problem at a class, anticipating everything a class of students might do with a problem can be a tall order.


The candy pieces made a grid. The rectangles were congruent. Let's start there.

The candy pieces made a grid. The rectangles were congruent. Let’s start there.

The Hershey Bar Problem was unleashed for the first time to a group of students. Our department has agreed to have that problem be a common problem among all three geometry teachers and to have the other two teachers observe the delivery and student responses (I love this model, by the way).

The students did a lot of the things we were expecting. But, we also watched as the students took this in a directions that we never saw coming. The student began using the smaller Hershey rectangles as a unit of measure. One of the perplexing qualities of this problem is that the triangles are not similar or congruent. Well, the rectangles are both. So, as we watched, we weren’t sure what conclusions could be drawn, what questions the students might ask, or how strongly the class might gravitate toward this visually satisfying method.

We didn’t want to stop her. We weren’t sure if we could encourage her to continue. We just had to wait and watch. That causes anxiety. It feels like you aren’t in real control of the lesson.

Adding an auxiliary line changes the look of the problem, "How were we supposed to know to do that!"

Adding an auxiliary line changes the look of the problem, “How were we supposed to know to do that!”

In the end, most of what we anticipated ended up happening. The team trying to estimate rectangle grid areas ended up seeking a different method for lack of precision and everything got to where it was supposed to. The experience is valuable. But the anxiety is real.

This student was trying to make sense of the perimeters and areas

This student was trying to make sense of the perimeters and areas

And I suspect that the anxiety has a lot to do with why the textbooks continue to stay close at hand. When the structure leaves, the curriculum opens up. When the curriculum opens up, the task of planning and instructing becomes more stressful and (for a short time) more time-consuming.

If you are reading this and on the cusp of trying to move away from your textbook, please know that this is the right move. Your book is holding you and your students back. You can do this. I won’t say that there is less stress, but with more authentic lessons, there’s more authentic learning.

Mathematical Modeling: The Glass is Half-Full

Where is the horizontal half-way line?

Where is the horizontal half-way line?

By the time they get to me, the students in my calculus class have been given a chance to master a whole lot of math. Typically, though, they haven’t been exposed to many situations where the main challenge of the task is figuring out which types of mathematical tools will best model a problem, and thus, drive the method used to solve the problem.

Take, for example, the problem described here. This is a wonderful, challenging little task that seems so fascinatingly simple and yet becomes quite complicated quickly.

The task: draw a single horizontal line on the cup that represents the half-way line by volume. Almost as soon as I asked the question, you could see the wheels start spinning in the heads of the students.

"Well, it looks sort of like a cone, but it doesn't have a point."

“Well, it looks sort of like a cone, but it doesn’t have a point.”

Some took measurements and prepared to “calculate” it. But did they need a formula? How would they find it? What the heck kind of shape is this thing anyhow? How can we be sure out measurements were accurate?

Making sure measurements are accurate

Making sure measurements are accurate

Some were going to draw it onto paper. But how to they model it? Can they use a 2-D cross section? Which cross section do we use? What do we do with it now that we have it?

Modeled as a two-dimensional shape

Modeled as a two-dimensional shape

Some figured to guess and check. I mean, the half-way is probably going to be somewhere in the middle. There’s not THAT many different values, really. But what do you guess? Do you have to guess more than one thing? How do check your guess to see if it is right?

And all groups had to deal with the question: When you have finished up the work on the page or on the calculator, how do you accurately transfer it back to the cup?

So, let’s get it out into the open: being able to mathematically model a problem that exists in your hands with math that has always existed in a book is not something that comes naturally to most people. In addition to the content, students need to practice modeling the mathematics. They need to learn what the book math looks like when it is in their hands. Jo Boaler (Stanford Math Ed Professor) has a wonderful line about this.

“…students do not only learn knowledge in mathematics classrooms, they learn a set of practices and these come to define their knowledge. If students ever reproduce standard methods they have been shown, then most of them will only learn that particular practice of procedural repetition, which has limited use outside the mathematics classroom” (pg. 126, see bottom for proper citation).

It’s as if the math experiences we are giving most students in class are the kinds of experiences that will do them the least good outside class.

Authentic mathematical modeling requires giving students a task with a simple and clear goal and then letting them decide what kind of math will help to complete the task. The decision is an incredibly important part of the process. They must recognize the variety of available tools, have to choose which ones will work, and of those ones, which one is the best choice.

The #MTBoS is doing a great job of providing tasks of this kind of a nature (Like here, for example… or here, as another example). They are plentiful, well-done, and FREE! Give them a shot and see what happens. We owe it to our students to provide them opportunities to take the math off of the pages of the book and let them see what it looks like when it shows up in their hands.


Boaler, Jo (2001). “Mathematical Modelling and New Theories of Learning.” Teaching Mathematics and Its Applications. Vol. 20. No. 3, p 121-128.

Circles from Cedar Street

A sloppy bit of construction work makes for an interesting geometry question.

A sloppy bit of construction work makes for an interesting geometry question.

I was driving to the grocery store. This particular trip took me down Cedar Street. I drove past this manhole cover. It caught my eye in such a way that I decided to pull into a nearby parking lot and, when the traffic cleared, tiptoe out to the middle of the five lane road and snap a photo of it.

So, my mind instantly went straight to rotations. (Which is on my mind because transformations are Unit 1 of the Geometry Course that I start teaching in, like, two weeks.)

What if I started out rotations by showing this picture and simply asking the students how much of a rotation would fix the yellow lines.

My goals would be for the students to explore how to investigate an apparent rotation, learn how to visually represent a rotation, and struggle through the task of explaining it out loud to another person.

It would be okay with me if we made it to the convenience of using degrees as a descriptor of how much something is rotated. That would be up to them. I do suspect that after a short time of “about this far” and “about that much” they’ll like to find something to ease the trouble of explaining the transformation.

If you can think of a way to frame this learning opportunity better, please make me a suggestion. I feel like this is a good opportunity that I don’t want to waste.

Penny Circles

This discussion represents the final Makeover Monday Problem of the Year. I must admit, I found this problem to be easily the most engaging for me simply as a curious math learner. (Here’s  the original problem posted by Mr. Meyer.)

Now, I will admit that this is going to be more of a discussion of my experiences exploring this problem and, if you get lucky, I might come up with a recommendation somewhere toward the end.

The problem presents a rather interesting set up: filling up circles with pennies, making predictions, modeling with data, best fit functions. Lots of different entry points and possible rabbit holes to get lost in.

First change was that my circles were not created by radii of increasing inches. For the record, I can’t quite explain why I chose to make that change. Instead, I used penny-widths. Circle one had a radius of one penny-width. Circle two’s radius of two penny-widths. Circle three’s radius… you get the idea.

It looked like this:

I started with 4 circles with radii based on penny width.

I started with 4 circles with radii based on penny width.

Note: I understand the circles look sloppy. I had wonderful, compass-drawn circles ready to go and my camera wasn’t playing nice with the pencil lines. So, I chose to trace them with a Sharpie freehand, which… yeah.

Next, I kept the part of the problem that included filling each circle up with pennies.

It looked like this:

Penny Area 1

Then I filled them with as many pennies as I could

Then I filled them with as many pennies as I could

Here’s where the fun began.

I saw a handful of different interesting patterns that were taking place. If we stay with the theme of the original problem, then we’d be comparing the radius of each circle to the penny capacity, which would be fairly satisfying for me as an instructor watching the students decide how to model, predict, and then deciding whether or not it was worth it to to build circles 5, 10, or 20, or if they can develop a way to be sure of their predictions without constructing it.

But, I also noticed that by switching to the radius measured in penny-widths, the areas began to be covered by concentric penny-circles. So, we could discuss how predicting the number of pennies it would take to create the outside layer of pennies. Or we could use that relationship as a method for developing our explicit formula (should the students decide to do that).

So, if I am designing this activity, I feel like the original learning targets are too focused and specific. I want the students to be able to use inductive reasoning to predict. Simple as that. If they find that using a quadratic model is the most accurate, then cheers to them, but this problem has so much more to offer than a procedural I-do-you-do button pushing a TI-84.

First, I’d start with them building their circles using a compass and some pennies. Build the first four and fill them in. I’m quite certain that the whole experience of this problem changes if I leave the students to explore some photos of the my circles. They need to build their own. Plus, that presents a low entry point. Hard to get intimidated lining up pennies on a paper (although, I have plenty of student intimidated by compasses).

Next, I think that I would be if I simply asked them to tell me how many pennies they would need to build circle five and to “prove” their answer, I believe we would see a fair amount of inductive reasoning arguments that don’t all agree. The students battle it out to either consensus or stale-mate and then we build it and test. It should be said, though, that as they are building the first four and filling them in, I’d be all ears wandering about waiting for the students to make observations that can turn into hooks and discussion entry points.

Then I would drop circle ten on them and repeat the process. This is where the students might try to continue to use iterations if they can figure out a pattern. Some will model with the graphing calculators (in the style the original problem prefers). I’m not sure that I have a preference, although I would certainly be strategic in trying to get as many different methods discussed as possible.

Then, when they have come to an agreement on circle ten, I’d move to circle 20 and offer some kind of a reward if the class can agree on the right answer within an agreed margin of error. Then, we’d build it and test (not sure of the logistics of that, but I think it’s important).

All that having been said, I see an opportunity to engage this in a different manner by lining the circumference of the increasingly-bigger circles with pennies so that the circle was passing though the middle of the pennies and seeing how, as the circles got bigger, how the relationship of the number of pennies in the radius compared to the number of pennies in the circumference. I suspect it could become an interesting study on asymptotic lines.

It just seems like this particular situation has, as Dan put it, “lots to love” and “lots to chew on.”

The Essentials of Project-Based Learning

On Thursday, I will be facilitating a collaborative session for teachers on Project-Based Learning, which, to be fair, is a topic that I have never considered comprehensively. I’ve never been asked to define it. I’ve never been asked to explain it and, quite frankly, until the organizer of EdCamp Mid-Michigan approached me to facilitate the session, I never considered myself a practitioner of it. I just tried to design lessons that were engaging and built authentic, lasting learning.

But, this EdCamp facilitator, who’s name is Tara, has known me for quite a while. We did our undergrad together. We did our Masters work together. She’s been on an interview committee that almost hired me. She’s aware of my shtick. Maybe she wants me to facilitate this through the lens of how I work. If that’s the case, then this takes on an extra degree of difficulty because I still feel like I have a lot of development left to do before people start emulating my approach.

Besides that, my approach isn’t really that complicated. For any activity I consider offering to the students, I simply try to ask a couple of questions.

1. What can I do to maximize engagement? (I’ve seen plenty of ideas that I have had flop simply because the students aren’t drawn in.)

2. What can I do to facilitate collaboration? (The most effective use of class time that I ever see is when a group of students are effectively working together to solve a problem.)

3. What can I do to create a problem that will provide a variety of ways to solve it? (If there is only one real method to solve it, then as soon as one student gets it, the “collaboration” will become that student communicating “the way to solve it” to everyone else. My favorite evidence of this is when I hear a few “I don’t get how they did it, but this is how we did it and the answer came out pretty close to the same.”)

4. What can I do to make sure that the solution(s) are approaching effective learning outcomes? (While it can be interesting to occasionally have a group find a way to solve (or estimate a solution to) a problem effectively in ways that circumvent my desired learning outcomes, if I am continually putting together problems that don’t push the curriculum the community is trusting me to teach, then my students will be missing something.)

My favorite examples of this process working well are The Lake Superior Problem, The Pencil Sharpener Problem, The Wedding Cake Problem, and the Speedometer Problem. In each case, engagement and collaboration were high. Multiple solutions were present and most of the solution techniques required the students to make sense of mathematical procedures that could be correct or could be incorrect. “Why this formula is better than that other one.” Or “neither of our answers are perfect, this this one is better because this process has less of a margin for error.” Stuff like that. These conversations provide great opportunities to move beyond the memorization of a formula and to push toward sense-making of how that formula is used effectively.

While I’m not sure if this is “by-the-book” project-based learning, I have seen improvements in my students’ learning through the lesson design process I described above. Does anyone have any advice for me? Questions for me to think about? Corrections? Obvious holes in my logic? I appreciate this community because of your willingness to share, so feel free to do so.