SMP 7 is a particularly interesting standard to look at in the high school curriculum because we can find structure in expressions, diagrams, graphs and more. This year I worked closely with the Algebra teachers in my district while we implemented a new curriculum. One problem in particular from our new curriculum is below. ( From Engage NY Algebra Module 4 Lesson 8 (Student View) )
There were additional problems that made use of the structure of a parabola in order to solve.
- Is f(4) greater than or less than -6? Explain
- f(-4)= -13. Predict the value for f(4) and explain your answer.
Towards the end of the lesson there was a section called Finding a Unique Quadratic Function. Below are some of the prompts from that section:
- Can you graph a quadratic function if you don’t know the vertex? Can you graph a quadratic function if you only know the 𝑥-intercepts?
- Remember that we need to know at least two points to define a unique line. Can you identify a unique quadratic function with just two points? Explain.
At one of the schools that I work at we spent two days exploring the structure of parabolas and questions like the ones above using Desmos.
Day 1 Activity: Broken Parabolas
Day 2 Activity: 1-3-5-7 Parabola Challenges
In the 1-3-5-7 Parabola Challenges students explored the symmetry of parabolas by locating missing points given a set of points on a parabola. For this lesson students only looked at parabolas with an a value of 1. We didn't use that language since it was an introductory lesson, but it allowed students to use 1,3,5,7 (etc.) pattern when comparing the differences in y-values.The hope was that this informal exploration would set students up to look for and make use of structure when they graph parabolas by hand later in the unit.
Having students reason through the problems using a pattern can also make for a great error analysis activity. Some of the student work from Activity 2 is below. Each of these challenges started off with a set of blue points, and students were able to drag the red points to complete the parabola. They would then turn on the green function to check that it is going through all of the red and blue points. At the end there are also a couple of unique responses for challenges 1 and 2 from the 1-3-5-7 Parabola Challenges activity that would have been great to share with the class.
The original version of this activity had students entering coordinates into a table instead of dragging points. I thought this would help them focus on the patterns in a table of values as well, which could be an additional problem solving tool for them to utilize later in the chapter. This turned out to be too challenging for the group of students that I initially worked with. Adding points to a table of values using a pattern requires strong number sense, and is a different skill then having students use a pattern to add points to a coordinate grid. Here is the original activity in case you'd like to take a look.
Focusing on SMP 7 in the planning of these activities shaped them in ways that led to increased reasoning and discourse. Of course this is not the only way to increase mathematical reasoning, but definitely worthy of some focus this summer.
Footnote: I also wanted to thank Silicon Valley Math Initiative for an inspiring end of the year session. Their summer focus is also on SMP 7, and we launched this work in our last session by finding examples of SMP 7 in the K-12 curriculum. I've been thinking about SMP 7 and seeing examples of it ever since.