# Demonstrating the Structure of Quadratic Functions with Desmos

I am a big fan of empowering students to look for and make use of structure in Algebra 2. This is most true for me as we work with functions, parabolas, and quadratics.  I’m writing this post about what I’m finding to be an indispensable tool for helping students quickly learn about the structure of the equations of quadratic functions. This tool is easy to use. Simply project the Desmos calculator (use the links below) and activate the sliders.

One of the many great things about Desmos is some of their built in functions on the calculator. Like this one, using vertex form of a parabola:

In this window, you can activate the sliders* individually to demonstrate to students (and share with your math team)  how a, h, and k affect the parabola. You may want to stop the slider and manually slide a to values you want to emphasize with the class (a = 2, 1, 1/2, 1/3, 0, -1/3, -1/2, -1, -2 for instance).

*To activate the sliders, click on the arrow buttons in rows 2, 3 and 4. To stop them, click again, or manually move the slider to any spot.

Next, move to standard form, which is really interesting.

I suggest you first let c slide and have students watch as the parabola moves up and down. Ask them whether the shape is changing. Some will think it is, but it’s just an optical illusion. Tell them to look again.

Then, stop c and let a slide. Kids can see how the parabola stretches, shrinks and reflects just as it did with vertex form.

Last, the fun one. Ask them to predict and then tell their partner/group what they think will happen when b slides. Will the shape change? Will it move up, down, left, right? Then, activate the slider.

This is where the math just gets cool. Ask them, as they watch the motion, “What is the path of the vertex?” (it travels along a parabolic path); “What is happening to shape of the graph?” (nothing, it stays the same); and, “What is happening to the y-intercept?’ (the parabola travels through the point (0, c) and the intercept doesn’t change).

I found this to be so helpful to me as a teacher and to students to see quickly what the structure of these equations do. To get to them and many others, just click on the bars at the top left corner of the window for the desmos calculator. There are all kinds of great functions to work with. Here’s a picture I made in paint – screen shot, save in paint, edit with brush – to help you find the drop down menu.

P.S. I need to create a note sheet for this where they summarize these structures and the impact of the key components. Next week. Yep, next week. 🙂

# Last minute quiz inspiration

Yesterday, I suddenly decided on a new quiz format. I had been writing a quiz for my Honors Algebra 2 class and I just didn’t like it. It wasn’t interesting or challenging. I really didn’t want to make a second version (my kids sit at tables), and was hoping for several days that some inspiration would hit. Our text has a set of alternate assessment questions, but they are a bit involved.

So, in the 5 minutes before class started, inspiration hit like a tons of bricks.

I let them use the alternate questions, and work in pairs. There are 6 students at a table group and we were covering two chapters. I gave them packets of the questions. There were about 7 questions for Chapter 1 and 6 questions for chapter 2. The guidelines were that they had to answer one question from each packet and couldn’t answer the same questions as the people at the table group. So, that’s a total of 6 questions for the table, three from each chapter, two for each pair of students.

To make it an actual quiz, they couldn’t use notes. They also couldn’t ask me questions. Actually, they could, but they would lose a point. Each question was worth 10 points, for 20 points total. Asking one question would still yield an A. But, no one asked any questions. The kids were engaged and worked steadily for about 35-40 minutes. Most finished, no problem.

I called time at 45 minutes. Some students hadn’t finished. I gave 5 more minutes. However, a couple of groups didn’t get to the second question or had just started it. Uh-oh.

So, as this is a group of motivated, grade-stressed students, I allowed them to come back at lunch or after school or during our tutorial time to finish. They appreciated it, so we were good.

The best part, was in the ask for feedback about the quiz format.

I gave them three prompts:

• Partner quiz again? yes/no
• This would have been better if…
• This was good for…

They unanimously liked the partner quiz because they had another brain to work with. Asking for feedback is gold! Making myself vulnerable was scary. Here I had changed up the quiz in the last few minutes, kids didn’t finish, they were afraid to ask a question even when it would have gotten them to the finish.

Would I do it again? Yes! Overall, it was a positive practice for them and for me. In fact, I’m doing it again today with my other section of that class. I’m happily incorporating their feedback with what I observed to make the following changes for the next class and next partner quiz. Here’s my list:

They asked me to:

1. Make more copies of the questions – it slowed them down to have to share.Yes. Done. Easy.
2. Allow questions. Well, I’m thinking no on that, because I think they will ask me a million questions. So, modified practice: they can ask the question. If it’s a fair question, I will guide with no point deduction. If it’s a question about not understanding the content, then I will take a point if I answer. They can ask the question, then I will answer or respond with, “Yes, I’ll answer, but it will cost a point.” Then they can decide if they want the answer.
3. Give more time. No, but I will advise students to read the entire question before choosing (most have multiple parts) and remind them that they can change the question if they get really stuck. Also, I will be more active in making sure everyone is employing strategies to finish on time.
4. No one mentioned this in the feedback, but I didn’t give them a time frame before they started. I wasn’t sure how long it would take. When half the class was finished, I announced 10 more minutes. I should have circulated a bit to check on their progress at around 20 minutes to let students know they should start on their second question within 5 minutes, so they have time to finish.

Now, I just have to grade them. That’s nice too, because I only half the number of quizzes to grade. Another teacher benefit from the partner quiz.

Please comment below with questions or ideas or practices you have tried. If you want to know more about the course or text, send me an email.