Features of a Parabola
Lesson 9 of 21
Objective: SWBAT identify the roots and the vertex on the graph of a quadratic function.
Today's opener is about the three "green functions" from the Quadratic Functions Gallery Walk that kicked off yesterday. By referencing work that kids have already done, I hope to give everyone a chance to use what they've got, to share this knowledge with the class, and to help our community build an understanding of quadratic functions.
The instruction asks, "What is the 'lowest point' for each function?" I expect that students will be able to look at their work from yesterday and to identify these points. On the side board, I make a table in which we can record the lowest point and roots for each function, and I ask for students to share what they've got. When someone says that the lowest point for Function A is at (-2, -4), I ask if anyone else agrees or disagrees, and we reach consensus for the next two functions in the same manner.
With the next slide, I ask if everyone can identify the roots of each function, and we follow the same steps. At minimum, I want students to be able to identify roots by looking at a graph, and I watch closely to see who can and cannot. Depending on how confidently my students can approach this task, I might ask them to factor each expression to see that the roots are what we expect them to be. If that doesn't happen now, we'll get to it soon; tomorrow's lesson is about using what we know about the features of a parabola to more efficiently produce a graph.
There is a lot to notice about the relationships between a quadratic function, its vertex, and its roots. I don't rush into naming any of these connections, but I do leave room for students to say what they notice, and that helps us build upon what we know.
The opener leads neatly into continued work time on the gallery walk. Please see yesterday's lesson for details on how I get students started on this activity. I tell students to pick up where they left off and I add one new instruction: everyone should label the roots and the lowest point, "which is called the vertex," I say, on each of their four graphs. To get everyone started, I provide this example for Function A. For some students, this is a nice confidence boost because they see they've already got it right. For struggling students, it always helps to see another example. Either way, this is a chance for kids to see exactly what I mean by labeling the vertex and roots, and they're able to do the same.
On today's lesson slides are the green functions (these were the focus of today's opener) and the blue functions, just in case we have any reason to discuss them as a class. With most of my classes, students are ready to get to work, and we won't touch these slides, but they're there just in case everyone gets stuck.
The value in this activity is that students can really get a feel for the shape and behavior of a parabola. As I wrote yesterday, the amount of arithmetic required may make for some slow going. It's my job here to make sure that students are building enough of an appreciation for how these graphs work that they're able to embrace the shortcuts that we'll develop tomorrow.
I give students until there are about five minutes left in class to finish their work. When students finish early, they can choose between two extensions, which are outlined in the next section of this lesson.
If students finish the Gallery Walk with time to spare, I collect their work and tell them they have two choices of what to do next.
Option #1: Add Your Work to the Gallery
There are stickies notes posted on each function in the gallery walk, and I invite students to take a sticky and make a table of values or a graph to post as an exemplar for each each function. I always keep a supply of 11x17 inch ledger paper and colored pencils in my room, and there's plenty of graph paper available. Students can use these supplies to complete the gallery, which will serve as a great reference for the rest of the unit.
Option #2: Complete Quadratic Functions in Three Forms
Many students still have to finish up the Quadratic Functions in Three Forms activity that preceded the Gallery Walk. When a student turns in today's work, I ask them where they stand on that activity. I ask if this assignment makes more sense now that the gallery walk is done, and suggest that they sketch a graph of each functions, again labeling the key features of each graph.
With five minutes left in class, I call everyone to attention and post the exit task, which is on the last slide of the lesson notes. Students are given the equation for a quadratic function, and asked to "make a quick sketch" and label the roots, the vertex and the y-intercept.
I expect to see a wide spread among what students know and can do with this task. No matter what kids have done on their gallery walk, here's a chance for them to show what they understand. Everyone has done a different amount of work over the last two days, but here's the bar that I expect everyone to reach.
The short amount of time students have to complete this exit task means that it's all about how efficiently they can work. If a student has developed some shortcuts of their own, they will use them here. If they must make a table of values, then they'll have to work quickly. Even when students can't produce a perfect graph, they're often able to accurately label the roots and vertex. Every partial solution I get gives me insight into the next steps I'll take with each student.
We'll end class like this again in about a week, which is exciting because it will make it clear to students how much they've learned by that point.