# Category Archives: Technology

#### Using Technology to Make Math Stick

How might we enable students to grasp mathematical concepts and make their learning durable?  One approach is to use the sequence of Action-Consequence-Reflection in lesson activities:

• Students perform a mathematical action
• Observe a mathematical consequence
• Reflect on the result and reason about the underlying mathematical concepts

The ACTION can be on a graph, geometric figure, symbolic algebra expression, list of numbers or physical model.  Technology can be used in order to have a quick and accurate result or CONSEQUENCE for students to observe.

The REFLECTION component is the most important part of this sequence; without this, students might not pay attention to the important math learnings we intended for the lesson.  They might remember using calculators, computers, ipads, or smartboards, but not recall what the tech activity was about.  And if they did learn the concept in the first place, the process of reflection helps make the learning stick—it is one of the cognitive techniques shown to make learning more successful.*

Students can reflect in many ways: record results, answer questions, discuss implications with classmates, make predictions, communicate their thinking orally or in writing, develop proofs and construct arguments.  The intended (or unexpected) learnings should be summarized either individually or as a class in order to solidify the concepts, preferably in a written form. **

In my one-on-one work with students, we often fall into the “procedural trap” in which my students just want to know “what to do” and don’t feel that the “why it works” is all that important (I’ve written about this before here). Also, our time is limited with many topics to cover.  But this past week, I was able to sneak in some Action-Consequence-Reflection with two students because they had mastered the prior material and were getting ahead on a new unit. It was a great opportunity to have them discover a concept or pattern for themselves, far better than simply being told it is true.

For each of these, I used a simple REFLECTION prompt:  What do you observe?  What changes?  What stays the same?

Student #1: Polynomial Function End Behavior, Algebra 2 (or PreCalculus)We used a TI-84+CE to investigate the polynomials.  We began with the even powers on a Zoom Decimal window, and my student noticed that higher powers had “steeper sides”.  I asked “what are the y-values doing to make this happen?” and we noticed the y-values were “getting bigger faster”.  We then used the Zoom In command to investigate what was going on between x = –1 and x = 1, and noticed that higher powers were “flatter” close to the origin because their y-values were lower.

Why did this happen? Take x = 2 and raise it to successive powers, and it gets bigger. Take x = ½ and raise it to successive powers and it gets smaller. We confirmed this with the table:

Setting the Table features to “Ask” for the Independent variable but “Auto” for the Dependent made the table populate only with the values we wanted to view. Fractions can be used in the table, and we used the decimal value 0.5 for clarity. Another observation was that the graphs coincided at three points: (1, 1), (0, 0) and (–1, 1).

In fact, none of this was what I “intended” to teach with the lesson, but it was mathematically interesting nonetheless, and my student already had a deeper appreciation for the graph’s properties. We moved on to the odd powers, and the same “steep” vs. “flat” properties were observed:

Then I asked my student to consider what made the graph of the even powers different from the graph of the odd powers, and what about them was the same, finally getting around to my “lesson”.  He noticed that even powers had a pattern of starting “high” on the left and ending “high” on the right, while odd powers started “low” on the left but ended “high” on the right.  We made predictions about the graphs of x11 and x12, to apply our understanding to new cases.† Then we moved on to the sign of the leading coefficient: when it is negative, our pattern changed to even powers “low” on the left and “low” on the right, with odd powers “high” on the left and “low” on the right.

All of this took just a few minutes, including the detour at the beginning that I wasn’t “intending” to teach.

Student #2: Interior and Exterior Angles of a Triangle, Geometry

We began with a dynamic geometry figure of a triangle which displayed the measurements of the three interior angles and one exterior angle.  I asked my student: “What do you notice?” and “what do you want to know about this figure?”  We dragged point B around to make different types of triangles.

This motivated my student to wonder about the angle measures; he was familiar with Linear Pair Angles, so he noticed that ∠ACB and ∠BCD made a linear pair and stated they would add up to 180°.  I then revealed some calculations of the angle measures, which dynamically update as we changed the triangle’s shape (the 180° in the upper right is the sum of the 3 interior angles).  What changes? What stays the same?

We noticed that both sums of 180° were constant‡ no matter how the triangle was transformed, but the sum of the 2 remote interior angles kept changing, and in fact, matched the measure of the exterior angle.  My student recorded his findings in his notebook, and then I asked, “can we prove it?”.  It was easy for us to prove the Exterior Angle Theorem based on his previous knowledge of the sum of the interior angles and the concept of supplementary linear pairs.  This student loved that he had “discovered” a new idea for himself, without me just telling him.

Even though these concepts are relatively simple, I feel that using a technology Action-Consequence activity made the learning more impactful and durable for my students, and I believe it was more effective than just telling them the property I wanted to teach. It took us a few more minutes to explore the context with technology than it would have to simply copy the theorems out of the book, but it was worth it!

Notes and Resources:

*For a full elaboration of cognitive science strategies for becoming a productive learner (or designing your teaching to enhance learning), see Make It Stick: The Science of Successful Learning by Peter C. Brown, Henry L. Roediger & Mark A. McDaniel, 2014.  Website: http://makeitstick.net .

**Written summaries allow students to Elaborate and Reflect on the learning, two more of the cognitive strategies.  In addition, by insisting that students record the results of the work, the teacher sends the message that the technology investigation comprises important knowledge for the class.

†Making predictions is a way to formatively assess my students’ understanding.  It also is a form of Generation, another cognitive strategy that makes the learning more durable.

‡This is an example of an invariant, a value or sum that doesn’t change, which are often important mathematical/geometric results.

Here are the two activities discussed in the post. Note that the Geogebra file for Power functions has the advantage of having a dynamic slider, but students won’t view the graphs at the same time, so won’t notice the common points or the graph properties between –1 and 1.

# Searching for Structure

Recently, I read on Twitter some teachers’ frustration with students who just want to know the quick procedures to do the math at hand and don’t have much interest in the meaning of the underlying concepts.  I often come across this dilemma in my one-on-one work with students; in this tutoring role I especially feel the pressure to teach the “how-to” for an upcoming test and don’t always have the time to explore the “why” with the student.  I wrote a bit about this tension before in this post.

Another conversation on Twitter was specific to Algebra 2, about how to build on past knowledge even when some/all of the students seem not to remember that past knowledge.  How might we deepen students’ understanding and not simply retread the procedures?

I was faced with these dual dilemmas when I worked with a student this week reviewing Complex Numbers and Quadratic Equations for an upcoming test.  My approach: pay attention to mathematical structure.

A. Fractions involving imaginary numbers:

These three examples, examined together, allowed us to explore how to handle a negative value in the radicand (“inside the house”) and also how to handle a two-part numerator* with a one-part denominator.  Once the imaginary  i  was extracted and the radical simplified as much as possible, we took a look at when we could and couldn’t “simplify” the denominator.

I wanted to help my student avoid the common mistake of trying to “cancel”** when you can’t.  We used structure to explain.  When there is a two-part numerator and a one-part denominator, you can do one of 3 things:

“Distribute the denominator” to make two separate fractions.  I find this is the most reliable routine to avoid mistakes.

Divide “all parts” by a common factor.

Factor a common factor (if any) in the number, then simplify with the denominator.

{*I wasn’t sure if the numerators qualify as “binomials” since they are numeric values, but my student and I discussed how they have two terms on top and one term on bottom, which can be challenging to simplify.  This structure will be encountered later when solving equations using the quadratic formula.}

{**I have avoided the use of “cancel” since I became more familiar with the “Nix the Tricks” philosophy of using precise mathematical language and avoiding tricks and “rules that expire”.  See resources below for more on this.}

B. Operations with complex numbers:

Again, we looked at a set of three problems to examine structure, which leads us to the appropriate procedures:

What is the same and different about #10 and #11?  What operation is needed in each?  Which is easier for you?

What is the same and different about #11 and #12?  What do you call these expressions:  4 – 5i and 4 + 5i ?  If you notice this structure, how does the problem become easier?

This led to a fruitful discussion of combining “like terms”, what is a “conjugate”, and whether it mattered if the multiplication was done in any particular order.  My student had been taught to always list answers for polynomials in order of decreasing degree, as in x2 – 2x + 1, so he was writing any  i2  terms first.  This isn’t wrong, but the rearranging of the order of the multiplication could have caused a mistake, so we talked about whether  is a variable or not, and when might it be helpful to treat it like a variable.

By noticing the structure of conjugates and why they are used, we got away from merely memorizing math terminology and instead added to conceptual understanding.

C. Using the discriminant

The discriminant is one of my favorite parts of the quadratic equations unit!  Students must pay attention to the structure of a quadratic equation (is it in the standard form ax2 + bx + c = 0 ?) before using the discriminant to give clues about the number and type of solutions.

Rather than memorize what the discriminant means, look at where it “lives” in the quadratic formula.  It is in the radicand, which is why a positive value yields real solutions and a negative value does not.  The radical follows the ± , which is why nonzero discriminants give two solutions (either a real pair or a complex pair).  And the two solutions are conjugates of each other, something that I hadn’t really thought about when I got real solutions using the quadratic formula.  (And there is a nice surprise when you examine the two parts of the “numerical conjugates” and relate them to the graph of the quadratic. See note below for more on this.)

I recently read this post about one teacher’s success having students evaluate the discriminant first, then tackle the rest of the quadratic formula.  Her strategy integrates the use of the discriminant with quadratic formula solving, instead of making it a stand-alone procedure.

Calculator Note: when evaluating the Quadratic formula on the TI-84+ family of calculators, use the fraction template    to make the calculator input match the written arithmetic.  Press ALPHA then Y= for the fraction template, or get it from the MATH menu.  Then edit the previous entry for the second solution (use the UP arrow to highlight the previous entry and press ENTER to edit).  Here is #26 from above:

Another Calculator Note: the TI-84+ family in a+bi mode can handle the addition and multiplication questions #10-12, so if you are assessing student proficiency on these skills, have them do it without using the calculator.  The color TI-84 Plus CE can operate with an imaginary number within the fraction template, such as questions #4-6 and anything with the quadratic formula.  You can use either the  i  symbol (found above the decimal point) or a square root of a negative number.

However the B&W TI-84+ can’t use an imaginary number within the fraction template.  Use a set of parentheses and the division “slash” for this to work:

Notes and Resources:

Nix the Tricks website and book: nixthetricks.com.  And lest you think that “Distribute the denominator” is yet another trick, consider this:  The fraction bar is a type of grouping symbol (like parentheses) and it indicates division.  Dividing is equivalent to multiplying by the reciprocal.  So the “distribute the denominator” work for #4 above is also this:

Three articles about “Rules That Expire” have been published in the NCTM journals.  Currently all three are available as “FREE PREVIEWS” on the website.

“Look for and make use of structure” is one of the Standards for Mathematical Practice (SMP #7) in the Common Core State Standards found here: http://www.corestandards.org/Math/Practice/

The “nice surprise” about the solutions to a quadratic equation written as “numerical conjugates” and their relationship to the quadratic graph was pointed out to me by Marc Garneau.  His post here gives more detail and a student activity to go with it.

Thanks as always to the #MTBoS and #iTeachMath community on Twitter for great conversations!

# Fun Features of the TI-84+ Family

Recently, I was a panelist for a TI Calculators Webinar that happened to follow a new Operating System release for the TI-84+CE color calculator and its accompanying Apps and computer software.  The new calculator features were not our primary focus, but since OS 5.3 was just released, we tried to highlight them when appropriate. This post summarizes a few features of the new OS version 5.3; I want to share in more detail these fun features that will help my teaching and my students.

1.New shortcut key for the fraction template. I use the fraction template    to make the calculator inputs match the math notation.  It has been available for the entire TI-84+family for several operating systems.  Press ALPHA-Y1 to access the shortcut menu for the fraction and mixed number templates. On the color versions of the TI-84+, it is also found in the MATH>FRAC menu.

And now, there is an even faster way on the TI-84+CE: press

2. Piecewise Function Graphing now allows entry that looks like the textbook! Press MATH and select B. piecewise. Choose the number of pieces and then enter them using the inequality operators in the TEST menu (2nd MATH) or the CONDITIONS submenu.  Discuss with students whether it matters which piece comes first in the piecewise definition.

You might notice that in Y= the viewable area is limited when entering a piecewise function.  If desired, you can enter the piecewise function on the Home Screen and store it to one of the graphing function variables.  You will need to start and end the piecewise function with the quotation symbol (press ALPHA and the PLUS button).

Don’t have a CE but want to graph piecewise functions?  Instructions are found HERE and this method can prompt a rich discussion of how to use a logical operator in a math expression (the inequality statement will represent 1 if it is TRUE and 0 if it is FALSE).  Try TRACING the piecewise graph.  Where does the Y-value exist and not exist?

I like using piecewise functions on the calculator: it enables a graphical confirmation of a complicated algebraic expression, and that helps my students build their understanding.  It also gives us access to many real contexts for problem-solving.

3. Updated Transformation Graphing App. The newest Transformation Graphing App allows TWO transformable functions in Y1 and Y2 plus you can graph other static functions in Y3 to Y0 and up to three StatPlots.  You still use the four parameters A, B, C, D and you can now access several stored parent functions for lines, quadratics, cubics and trigonometry.

I like to challenge students to “Match the Graph” with a static function graph whose equation I haven’t shared (see below left, can you transform the blue graph to match the pink one?).  Or put data in a StatList and transform a function for a best fit curve.

It is now easier to move back and forth between the graph and the SETUP screen, and the “TrailOn” feature has moved to this more logical location [it was available in prior versions of Transformation Graphing, accessed from the FORMAT menu by pressing 2nd ZOOM.] See above right for the trail of quadratics.

And the entire Transformation Graphing process is faster than it was before (be patient if the calculator seems slow to respond and check for the “busy” indicator in the upper right corner of the color calculator screens).  HERE is a “How To” file for the Transformation Graphing App.

4. Easy storage of a Tangent Equation. When drawing a Tangent line to a graph, a MENU can be accessed using the GRAPH button (before entering a point of tangency) to store the equation directly to Y=.  This makes it easier to examine the equation of the tangent line in relation to the equation of the original function.

Entering the X-value for the point of tangency can be done by entering a value with the numeric keypad, or tracing to the desired point.  I prefer using the ZOOM DECIMAL window for “friendly” trace increments.

5. Finally: updating to a new OS is easy. You need a USB-calculator cable or a calculator-to-calculator cable.  Instructions are HERE and the OS is a free download from the TI WEBSITE.  Use the (free) TI-Connect™ CE Software or link to an already updated calculator.  For the new OS 5.3 for the CE calculator, there is a “Bundle” file that updates the OS and the Apps at the same time.

*Keep in mind that all the feature enhancements have alternatives for older OS versions. And even if your classroom has a mix of TI-84+ family devices, the TI-SmartView™ emulator computer software displays 3 distinct environments, so you can demonstrate in the CE emulator to take advantage of the features for the whole class.

6. Save Emulator State is back!! (I almost forgot to mention this) The TI-SmartView™ CE software NOW has the ability to “Save Emulator State” so the teacher can save work where you are when the bell rings at the end of the period and you can open it back up when that class returns the next day.  Or you can prepare your SmartView calculator in advance with your functions, lists, programs, etc. so that everything is loaded efficiently when you need it.  Instructions are HERE for using Emulator States.

Enjoy the new and old fun features! Reach out to me if you have any questions.

Resources:

The  “Making Math Stick” Webinar On-Demand is HERE and the activities discussed are HERE.  The new calculator features were not our primary focus, but since OS 5.3 was just released, we tried to highlight them when appropriate.

A great summary of some not-so-new features of the TI-84+ Family was written by my webinar co-panelist John LaMaster and is found HERE.

# In The Zone

I attended the Teachers Teaching with Technology (T-cubed) International Conference this past week in Chicago, and my four days were chock-full of thought-provoking sessions and conversations.  As expected, there was much talk about technology in math and science classes, but there was also a great deal of discussion concerning thinking about teaching and learning in math and science classes.  Here are some of my take-aways:

1. Get out of your comfort zone into the “learning zone.” In order to learn something new, get out of established routines (about doing math, about teaching math) and try another technique or perspective.  I pushed myself to learn about topics that are not my specialty, things I might have otherwise avoided.  I tried coding some calculator programs, tackled STEM/engineering design projects, learned a bit of 3D graphing, and brushed up on statistics.  Some things came easily, and other new skills were quite difficult.  At one point in a STEM session, I declared that the project was “really hard”, and sat back to watch others.  I was urged to continue by the presenters and fellow participants, and we worked together to complete the task.  I gained confidence because they had confidence in me, and was able to achieve something I thought might be beyond my abilities.  I was really glad I persevered in the task, and had acknowledged that it was “hard” but not “too hard.”

2. Productive struggle takes time. One of the eight Mathematical Teaching Practices in NCTM’s Principles To Actions (2014) is to “support productive struggle in learning mathematics.” In one of the sessions, presenters Jennifer Wilson and Jill Gough had us work on a difficult geometry problem, asking us to:

• Allow for “individual think time.” Please don’t steal another student’s opportunity to think by talking too soon.
• Go beyond getting the answer. What can you show about how you make sense of the problem?
• Work with it some more. Can you find another way? Can you relate your solution methods to each other, or to another person’s method?

I was surprised by two things that happened in this session.  First, as the presenters circled around the room reviewing our progress, they didn’t evaluate our work or tell us if we were on the right track.  When Jennifer suggested that I keep working—which I interpreted to mean that I had made an error in my reasoning—my solution was actually correct.  I realized later that taking more time to work had been advantageous and it had spurred me to find alternative methods.  A teacher saying to a student “work on this some more” is not the same as “you’re doing it wrong.”

The second big surprise was how long the process of struggling toward a solution took us.  I thought perhaps we had been working for ten or fifteen minutes (we are math teachers, after all, so I expected we would find solutions quickly).  In fact, we had been working for 35 or 40 minutes, which was astounding to me.  Time had seemed to slow down, and there wasn’t any race to finish up. I was able to really make sense of my multiple solution methods, and enjoyed pursuing more ways to solve the problem.

So if “promoting productive struggle” is a goal for your classroom, consider how to encourage it with your messages to students.  Think carefully about implementation: you need to invest ample time, but you will reap rewards in terms of the variety and depth of math concepts your students will uncover.

3. Be responsive to your professional peers. In his keynote, Timothy Kanold spoke about the professional community that exists in a school, and how a robust collaboration enhances the success of all students.  When teachers engage with each other, sharing best practices, kids experience similar (high-quality) learning environments even if they have different teachers.  When teachers operate independently, there can be substantial inequity between what students in different classrooms receive.

How might we apply this in our school settings? If there is a great activity you use in one of your courses, perhaps share it with colleagues teaching the same course.  If you employ technology to build mathematical understanding, try to make sure others have access to it as well.  You will benefit too:  discussing a lesson or teaching practice with a colleague will make your teaching repertoire more robust.  Attempting something new and different is easier when you have a like-minded peer who can give feedback (or possibly observe your lesson in action).

So what are my next steps? Returning home after an exciting professional conference always involves catching up and getting back to my regular teaching routines. But Jennifer and Jill commented that “closure” is not simply packing up at the end of class; instead I need to reflect on what I’ve learned, and thoughtfully consider how to put it into my practice.  I invite you to join me: take a risk, plan to do something new in the next few weeks, and find a colleague to collaborate with you as you move into the learning zone.

NOTES & RESOURCES:

For more about the T³ International Conference, search #T3IC on twitter or go to the Texas Instruments website.

To register for T³ summer workshops on Promoting Productive Struggle, STEM Projects, Coding, and Teaching Strategies for Success with Technology, go to the registration section of the TI website.

There is a full set of coding lessons and teacher guides available on the TIcodes section of the TI website.

The “Learning Zone” idea is related to Vygotsky’s “Zone of Proximal Development” (1978).  For more on scaffolding and ZPD, see Middleton, J. A.  & Jansen, A. (2011). Motivation Matters and Interest Counts: Fostering Engagement in Mathematics. Reston, VA: NCTM, chapter 9 “Providing Challenge: Start Where Students Are, Not Where They Are Not”.

More on “Promoting Productive Struggle” on Jennifer Wilson’s and Jill Gough’s websites.

# Rational Functions

We are studying Rational Functions, and I was looking for technology activities which would help students visualize the graphs of the functions and deepen their understanding of the concepts involved.  Previously, I had taught algebraic and numerical methods to find the key features of the graphs (asymptotes, holes, zeros, intercepts), then students would sketch by hand and check on the graphing calculator.  I wanted to capitalize on technology’s power of visualization* to give students timely feedback on whether their work/graph is correct, and avoid using the grapher as a “magic” answer machine.  I also wanted to familiarize students with the patterns of rational function graphs—in the same way that they know that quadratic functions are graphed as “U-shape” parabolas.

Here are three ideas:

Interactive Sliders

Students can manipulate the parameters in a rational function using interactive sliders on a variety of platforms (Geogebra, TI-Nspire, Transformation Graphing App for TI-84+ family, Desmos).  Consider the transformations of these two parent functions:

to become  and

to become

Each of these can be explored with various values for the parameters, including negative values of a.

Here are screenshots from Transformation Graphing on the TI-84+ family:

Another option is to explore multiple x-intercepts such as.

This TI-Nspire activity Graphs of Rational Functions does just that:

In a lesson using sliders, on any platform, I use the following stages so students will:

1. Explore the graphs of related functions on an appropriate window.  Especially for the TI-84+ family, consider using a “friendly window” such as ZoomDecimal, and show the Grid in the Zoom>Format menu if desired.  Trace to view holes, and notice that the y-value is indeed “undefined.”
2. Record conjectures about the roles of a, h, and k and how the exponent of x changes the shape of the graph.  This Geogebra activity has a “quick change” slider that adjusts the parent function from    to .
3. Make predictions about what a given function will look like and verify with the graphing technology (or provide a function for a given graph).

A key component of the lesson is to have students work on a lab sheet or in a notebook or in an electronic form to record the results and summarize the findings.  Even if your technology access is limited to demonstrating the process on a teacher computer projected to the class, require students to actively record and discuss.  The activity must engage students in doing the math, not simply viewing the math.

MarbleSlides–Rationals

A Desmos activity reminiscent of the classic GreenGlobs, MarbleSlides-Rationals has students graph curves so their marbles will slide through all of the stars on the screen.  If students already have a working understanding of the parent function graphs, this is a wonderful and fun exploration.

The activity focuses on the same basic curves, and it also introduces the ability to restrict the domain in order to “corral” the marbles.  Users can input multiple equations on one screen.

I really liked how it steps the students through several “Fix It” tasks to learn the fundamentals of changing the value and sign of a, h, k and the domains. These are followed by “Predict” and “Verify” screens, one where you are asked to “Help a Friend” and several culminating “Challenges”.  Particularly fun are the tasks that require more than one equation.

On one challenge, students noticed that the stars were in a linear orientation.

Although it could be solved with several equations, I asked if we could reduce it to one or two.  One student wondered how we could make a line out of a rational function.  Discussion turned to slant asymptotes, so we challenged ourselves to find a rational function which would divide to equal the linear function throw the points.  Here was a possible solution:

Asymptotes & Zeros

Finally, I wanted students to master rational functions whose numerator and denominator were polynomials, and connect the factors of these polynomials to the zeros, asymptotes, and holes in the graph.  I used the Asymptotes and Zeros activity (with teacher file) for the TI-84+ family.  It can also be used on other graphing platforms.

Students are asked to graph a polynomial (in blue below) and find its zeros and y-intercept.  They then factor this polynomial and make the conceptual connection between the factor and the zeros.  Another polynomial is examined in the same way (in black below).  Finally, the two original polynomials become the numerator and denominator of a rational function (in green below).  Students relate the zeros and asymptotes of the rational function back to the zeros of the component functions.

I particularly liked the illumination of the y-intercept, that it is the quotient of the y-intercepts of the numerator and denominator polynomials.  We had always analyzed the numerator and denominator separately to find the features of the rational function graph, but it hadn’t occurred to me to graph them separately.

A few concluding thoughts to keep in mind: any of these activities can work on another technology platform, so don’t feel limited if you don’t have a particular calculator or students don’t have computer/internet access.  Try to find a like-minded colleague who will work with you as you experiment with technology implementation, so you can share what worked and what didn’t with your students (and if you don’t have someone in your building, connect with the #MTBoS community on Twitter).  Finally, ask good questions of your students, to probe and prod their thinking and be sure they are gaining the conceptual understanding you are seeking.

NOTES & RESOURCES:

*The “Power of Visualization” is a transformative feature of computer and calculator graphers that was promoted by Bert Waits and Frank Demana who founded the Teachers Teaching with Technology professional community.  More information in this article and in Waits, B. K. & Demana, F. (2000).  Calculators in Mathematics Teaching and Learning: Past, Present, and Future. In M. J. Burke & F. R. Curcio (Eds.), Learning Math for a New Century: 2000 Yearbook (51–66).  Reston, VA: NCTM.

All of the activities referenced in this post are found here.  More available on the Texas Instruments website at TI-84 Activity Central and Math Nspired, or at Geogebra or Desmos.

For more about the Transformation Graphing App for the TI-84+ family of calculators, see this information.

GreenGlobs is still available! Check out the website here.

# Where Are You? I’ll Meet You There

I was so proud.  I had created a great technology activity to use in my Algebra 2 class, complete with a well-thought out lab sheet for students and their partners to work through and document their learning.  It was an exploration of slopes of parallel and perpendicular lines, with students being guided to “discover” the concepts involved.*

Questions for assessment involved different levels of cognitive demand, including creating their own sets of equations, paying attention to mathematical structure, and writing an explanation of their process.  The graphing calculators were ready and the students worked diligently through the class period.  The lesson was a success—everyone demonstrated their understanding of the mathematical objectives.

So what was the problem?  I asked a few students on their way out of class if they enjoyed the calculator lab activity since it was different from our “regular” routine.  They told me: “It was fine.  But Mrs. Campe, we all already knew about slopes of parallel and perpendicular lines.”

I had failed to properly pre-assess my students’ understanding of the concepts. I had wasted a full class period to cover something they had already mastered, when, instead, I could have been moving forward or exploring some other problem more deeply.  I didn’t check where my students were in their understanding before launching into my “great” activity.

Similar things can happen in my one-on-one work with students.  Since I am not in their classroom with them, when students arrive for a work session, I have to rely on them to tell me what their lesson and unit topics are.  Sometimes I go down a path that veers away from what they have done in class.  Some students resist conceptual explanations, wanting only the quickest route to the answer.  I have to push them to realize that learning the “why” behind a procedure helps them understand when and how to use it, and the conceptual background makes their learning more durable and leads to more success in math class.**

So what have I learned from these situations?

1.  It is vitally important to pre-assess and utilize formative assessment to know where my students are.  Class time is at a premium and I want to use it wisely.

2.  Don’t rely on students’ self-report of their understanding; require them to demonstrate their capabilities by doing problems, explaining a process, and answering “why” questions.

3.  Don’t use technology just because I have it.  It must further the lesson objectives and enhance student understanding.  The same warning goes for “fun” or “cool” lesson activities.

4.  Reflect on your lessons: ask yourself what went well and what needs improving so mistakes don’t get repeated.  And discuss with your colleagues, local and virtual. You will find lots of support in the MTBoS; one teacher commented to another on Twitter just last night: “Thx! I am always looking to improve my teaching!”

Mistakes, obviously, show us what needs improving. Without mistakes, how would we know what we had to work on?

Notes & Resources:

The technology lab activity on Parallel and Perpendicular Lines is here.  It was written for the TI-84+ family of calculators, but any graphing technology may be used.

*This lab activity is a “Type 1” investigation structure in that it guides students toward the desired mathematical knowledge, in contrast to a “Type 2” inquiry which encourages more open exploration.  Both types of lesson structures are effective, so match the level of exploration with your objectives.  More about this in McGraw, R. & Grant, M. (2005).  Investigating Mathematics with Technology: Lesson Structures That Encourage a Range of Methods and Solutions. In W. J. Masalski & P. C. Elliott (Eds.), Technology-Supported Mathematics Learning Environments: 67th Yearbook (303-318). Reston, VA: NCTM.

Another dimension useful in analyzing a lesson is type of teacher questioning.  “Funneling” questions guide students through a math activity to a predetermined solution strategy, while in “Focusing” interactions, the teacher listens to students’ reasoning and guides them based on where they are and what strategies they are employing, rather than how the teacher might solve the problem.  More in Herbel-Eisenmann, B. A. & Breyfogle, M. L. (2005). Questioning Our Patterns of Questioning.  Mathematics Teaching in the Middle School, 10(9): 484-489.

**Connecting new knowledge to what you already know (elaboration), building conceptual structures (mental models) and practicing what to do when (discrimination skills) are among the strategies for successful learning discussed in Make It Stick (Brown, Roediger & Mc Daniel, 2014).  See this website for more.

As a final thought, my title is misleading, because I don’t just want to meet the students where they are and stay there, I want to plan for appropriate challenges to take them beyond their current understanding.  There is great value in productive struggle, and choosing lesson components within the students’ “Zone of Proximal Development”.

# Function Operations

### Using Multiple Representations on the TI-84+

Algebra 2 students are studying function operations and transformations of a parent function.  My student had learned about the graph of and how it gets shifted, flipped, and stretched by including parameters a, h, and k in the equation.

Now he was faced with this question: how to graph  the equation in #58:

It didn’t fit the model of    so it wasn’t a transformation of the absolute value parent function.  He knew how to graph each part individually, but didn’t know how to graph the combined equation.  The TI-84+ showed him the graph with an unusual shape—not the V-shape he expected.

TIP: use the   button to access the shortcut menus above the  , , and   keys. The absolute value template is used here.

“Why does the graph look like this?” he wanted to know. We decided to break up the equation into two parts, using ALPHA-TRACE to access the YVAR variable names.* The complete function is found by adding up the two partial functions.

Then we looked at a table of values, to get a numerical view of the situation.  I remind my students that if they are unsure how to graph a particular function, they can ALWAYS make a table of X-Y values as a backup plan—it isn’t the quickest method to graph, but is sure to work.  To get the Y-values of the combined function, add up the Y-values for the partial functions, since .

Initially, we “turned off” Y3 by pressing ENTER on the equals sign, so we could view the partial functions in the TABLE. I asked the student what he thought the values in the next column should be.

He mentally added them up, and then we verified his thinking by activating Y3 and viewing the table again.

To further illuminate the flat portion of the graph, we changed the table increment to 0.1 in order to “zoom in” on those values.

TIP: While in the table,  press  to change the increment , or press 2nd WINDOW to access the TBL SET screen.Success! The TI-84+ provided graphical and numerical representations that deepened our understanding of the algebraic equation. This task had challenged the student, because it didn’t fit the parent function model he had learned, but he built on his knowledge of function operations to solve his own problem and help some classmates as well.  One of our approaches to learning is to “use what you know.”**

NOTES & RESOURCES:

*You can use function notation on the home screen to perform calculations with any function from the Y= screen. Access the YVARs from ALPHA-TRACE.

**Much has been written about Classroom Norms. See Jo Boaler’s suggestions here and my messages to students here.

For more about transformations on parent functions, see this information about the Transformation Graphing App on the TI-84+ family of calculators.

# Summer Assignment!

With the academic year winding down (and already finished for some), take a moment to think about what you will be doing this summer.  I’m sure you are planning to relax and refresh, but don’t neglect recharging your professional batteries…

READ A BOOK.  Is there one on your teaching bookshelf that you’ve been meaning to read?  Here are a few that I’ve read recently or have on my “Pedagogy and Learning” list for this summer:

• Make It Stick: The Science of Successful Learning by Brown, Roediger & McDaniel
• 5 Practices for Orchestrating Productive Mathematics Discussions by Smith & Stein
• Embedding Formative Assessment by William & Leahy
• Mathematical Mindsets by Boaler

If you have the opportunity, find a “buddy” or group and read together.  Try one chapter a week and discuss in person or via email.  Our Teachers Teaching with Technology cadre of instructors did book “discussion chats” this past year.  Here are some ideas and prompts to organize your comments on Embedding Formative Assessment and 5 Practices (thanks Jennifer!)

And since it is summer, I’m also planning to do some fun math reads.  Consider these, or maybe there are others you have your eye on (tell me in the comments!). The last two have the advantage that each chapter is a stand-alone essay, which is especially good if your attention span is shortened by summer distractions.

• How to Bake Pi by Cheng
• The Man Who Knew Infinity by Kanigel (now a major motion picture!)
• Here’s Looking at Euclid by Bellos (also a math columnist for The Guardian)
• The Joy of X by Strogatz (originally an essay series for The New York Times)

One more suggestion for your reading list is to catch up on an NCTM journal article you meant to read this year but didn’t have time to.  There are free previews of some articles on the website if you aren’t yet a member.

LEARN SOMETHING NEW (anything! Doesn’t have to be math-related.)  If you come back to school in the fall and share your experience with your students, they will see you as a learner and it may encourage their efforts.  Here are some ideas:

Watch a webinar.  Did you miss one this year you meant to join?  On-demand recordings are easily paused so you can take notes or try a problem yourself.  For example, Texas Instruments has an archive of their free webinars here.

Go to a workshop/class/conference. There are plenty of these available in person and online.  Your department or district may have local offerings.  The TI Teachers Teaching with Technology PD workshops are listed here, and include “virtual” workshops as well.  Jo Boaler’s YouCubed organization offers an online course for teachers “How to Learn Math” [info here].

For my Connecticut and New England colleagues, two great opportunities are nearby.  The T3 Northeast PD Summit is June 22 & 23 in New Britain, covering both the TI-84+ and TI-Nspire [info here and sign up here].  And the Geogebra Institute of Southern CT is holding their 4th annual conference in New Haven on August 16 [info here], including a pre-conference workshop August 15 for beginners.

MAKE A PLAN.  One of the best things for me about being a teacher is the chance to revise and improve my teaching practice on a regular basis.  Some years I taught the same course to more than one class, so each lesson got two or three tries in the same day (or week).  I reflected on how it went with the first group and made adjustments and improvements for the next class.  Remembering the details for the next school year is harder to do, so I would make quick notes right in my lesson plan to capture the changes I’d like to try in the future.  Here is the reminder I used as the last item on my “Lesson Plan Template”:

If you have notes from this year about lessons you’d like to modify, find them before leaving the building for the summer.

In 1994, Steve Leinwand wrote an article in Mathematics Teacher  “Four Teacher-Friendly Postulates for Thriving in a Sea of Change”.  One of them has resonated with me ever since then:  “It is unreasonable to ask a professional to change much more than 10% a year, but it is unprofessional to change by much less than 10% a year.”  While many of us try to change and improve our teaching each year (or are asked/mandated to implement new practices), change is challenging and daunting.  Leinwand suggests that teachers consider changing about 10% of what they do each school year, a very reasonable amount (just one new lesson every two weeks, or one unit out of the ten you teach).  What will be your 10%?  What topic/class/unit needs work?  Get a jump start this summer on something you’d like to teach differently than you’ve taught it before.

So, take this as your summer assignment: PICK SOMETHING you intend to do to learn and grow professionally this summer, along with your plans to decompress and have fun.  Let me know how it goes.  Have a wonderful summer!

NOTES & RESOURCES:

Leinwand, Steven. (1994).  Four Teacher-Friendly Postulates for Thriving in a Sea of Change. Mathematics Teacher 87(6):392–393. [Reprinted in 2007 during 100th anniversary of MT, with commentary by Cathy Seeley: Mathematics Teacher 100(9):580-583.]

More on  Recreational math books here: Math-Frolic.

# Problems With Parentheses

I have been noticing lately that my students are making mistakes involving the use of parentheses.  Sometimes parentheses are overused and other times they are missing, and errors are also made while using calculator technology.  Using symbols and notation correctly is part of SMP #6, “Attend to Precision”, and is also a component of mathematical communication, since so much of math is written in symbols.  I want my students to be efficient and accurate in their work, and I hope their notation supports their conceptual understanding. So I’ve been contemplating the purposes of parentheses…

Purpose #1: To Provide Clarity with Negative Integers.  Negative integers can be set off with a pair of parentheses for addition and subtraction, as in these examples, but the expression’s value is unchanged if the parentheses are not used:

1.    (–4) + 6 = 2
2.    6 – (–4) = 10

With an exponent on a negative integer, however, the parentheses are essential.  We are working on sequences and series in Algebra II.  When a geometric sequence has a negative common ratio, the explicit formula has a negative number raised to an exponent:

1.    The sequence  2, –6, 18, –54, … has explicit formula  An = 2·(–3)n-1

To convince my Algebra II students that the parentheses are required, consider  –32  vs.  (–3)2  on the TI-84+ calculator:

The calculator executes the order of operations: exponents are evaluated before multiplication. Since the negative sign actually represents –1 times 32, the 32  is evaluated first.  Although I prefer students to focus on conceptual understanding and not merely procedural rules, I say to “always use parentheses for a negative base”.

Purpose #2: To Specify the Base for Exponentiation.  Another class is studying exponents and logs, and students notice that using parentheses has mathematical meaning for the result.

1.    (2x)3    vs.   2x3
1. Each component of the fraction within the parentheses gets raised to the power; these are all different (and the TI-Nspire CAS handles them nicely):

Attending to precision is essential for students, and by doing three similar but different problems as a set, they get practice analyzing how the notation changes the results.

Purpose #3: To Properly Represent Fractions.  Fractions generally don’t need parentheses when written by hand, and I’m direct with students about my strong preference for a horizontal fraction bar rather than a diagonal bar when writing fractions on paper or on the board.

Complications can occur when students try to enter the fraction into a calculator without using a fraction template.  Pressing the DIVIDE button to create the “slash”, as in 3/4, has the advantage of connecting a fraction with the operation of division but the drawback of the diagonal bar.  For anything more complex than a simple fraction, parentheses are needed to “collect” the numerator and denominator so that the fraction is computed correctly.   For example:

1. Find the mean of these three test scores: 85, 96, 77.

1. Graph a rational function

Thankfully, fraction templates are readily available, so errors using parentheses are avoided.   On any TI-84+, set the mode to “MathPrint” and press ALPHA and Y= to access the template.  On a TI-Nspire, press CTRL and DIVIDE or select the fraction from the template palate.

This was especially useful for finding the sum of the following geometric series; notice the error on the first try due to missing parentheses, and then the corrected version:

And the calculator comes to the rescue! I encourage students to enter complicated expressions all at once.  Making separate entries for each part is taking a risk:

Purpose #4: To Indicate Multiplication. Probably the area in which I am observing the most “overuse” of parentheses is for multiplication.  At some time before students reach me in high school, they have been taught that in addition to using the × symbol to multiply, they can also use • , a raised dot. A third alternative is to use parentheses to indicate multiplication, especially for negative integers or to distribute multiplication over addition:

1.    (–4)( –6) = 24
2.    2x(x + 5) = 2x2 + 10x

I’ve seen some students “over-distribute” if they rely on parentheses instead of the raised dot for multiplication:

11.       (–4)(x)(3x2)  should be –12x3 ; however what if a student “distributes” the –4?

[One more pet peeve of mine: when students utilize the × symbol for multiplying even when using the variable x.  I strongly suggest that once they are in Algebra I, students should “graduate” to the raised dot  •  to symbolize multiplication.]

When using the Chain Rule in Calculus, students sometimes make the error of “invisible parentheses” and then lose them entirely in their subsequent algebraic simplification.

1. Find the derivative of (3x2 – 4x + 5)–2

Notice the missing parentheses for (6x – 4) and how the error carries through.

Purpose #5:  Operator Notations.  My final category of parentheses usage is as part of the notation of certain function operators.  Students are familiar with using parentheses in function notation f(x), where the independent variable x is the input for the function expression.  Other functions such as logs and trig functions can use parentheses to set off their “arguments”, and the calculator supports this use by providing the left parenthesis.  Entering the right parenthesis is optional on the TI-84+, but a good practice for students:

If students get in the habit of using the parentheses, it enables them to correctly apply the “expand to separate logs” and “condense to a single log” rule.  Here the parentheses are not “needed” to indicate the argument of the log, but helpful for this student.

1. Solve each equation:

And in these last two examples, the parentheses helps the student get the correct result:

1. Expand to separate logs:

1. Condense to a single log:

One final note: I want my students to harness the power of parentheses to support their conceptual understanding and mathematical accuracy.  Being precise about notation is not about “doing it my way” but instead about doing it in a way that helps them grasp the purpose of the symbols they use to clearly communicate their mathematical thinking.

NOTES & RESOURCES:

For more about the “loss of invisible parentheses”, ambiguous fractions and other common math errors, see this site.

For one teacher’s approach to using parentheses to evaluate function values, read this blog post: An Algebraic Oath.

And here is one teacher’s elegant and simple definition of parentheses: Parenthetically Speaking.

# Leap Years & License Plates

### Thoughts on Divisibility and Counting

I am always in search of good numbers. When I park in a commercial parking lot, I look for a space with a number that is divisible by 3. I like addresses and phone numbers which involve multiples (such as xxx-1696 since 16 x 6 = 96). I enjoy mathematical dates, like 11/11/11, 10/11/12 or 3/5/15.

So the year 2016 has been a good one so far, numerically speaking. In February, I noted 2/4/16 and 2/8/16 and 2/14/16 (you can do the math). And on 2/29/16, otherwise known as “leap year day,” I started thinking about how to determine if a given year is a leap year.

Leap years occur every four years in order to synchronize the calendar with the astronomical seasons. To be precise, they occur in every year that is exactly divisible by 4, however years that are multiples of 100 are NOT leap years, unless they are multiples of 400. And how can one look at a number and determine if it is a multiple of four? Simply examine the tens and the units digits; if that two-digit number is a multiple of four, then the larger number is also a multiple of four. So 2016 is divisible by 4, but 2014 is not.

The rules for divisibility are taught at a variety of math levels. I remember learning the rules for divisibility during a seventh grade math unit on bases other than 10. My children learned them in fifth grade while doing factors, multiples and prime numbers. The Common Core State Standards doesn’t mention them by name, but begins discussion of division in grade 3, and factors, multiples, and primes are contemplated in grades 4 and 6.

In my work with middle school and high school students, I find great variation; some students are skilled at divisibility rules and others are surprised to hear about them. Everyone knows how to tell if a number is divisible by 2 or 5 or 10. Many of my students think multiples of 3 should work the same way (they should end in 3 or 6 or 9) and although they may know the “finger trick” for the first ten multiples of nine, they haven’t considered how to test larger numbers. The rules for divisibility by 3 and 9 rely on the sum of the digits (in contrast to the rules for 2, 4, 5, and 10).

My favorite divisibility rule is the one I learned most recently; while doing KenKen puzzles, I wanted a method other than long division to determine divisibility by 7. The technique is this:

1. Chop off the units’ digit and double it.
2. Subtract this from the remaining number.
3. Continue this process until the result is 1 or 2 digits.
4. If the final number is divisible by 7, then the original number was divisible by 7 [Note that 0 is divisible by 7].

For example: 3052

1. Take the 2 and double it to get 4.
2. 305 – 4 = 301
3. Take the 1 and double it to get 2.
4. 30 – 2 = 28 which is divisible by 7.

In the same manner, 2016 can be shown to be divisible by 7. So 2016 is a very good year: it is not only a leap year divisible by 4, but is also divisible by 3, 7 and 9.

Can we use technology to help students test for divisibility? On any calculator, we can simply divide each proposed factor. For more efficiency, use the TI-84+ table with the function Y1 = (number)/x and scroll through the table looking for whole number results.

This can be impractical for very large numbers, but on the TI-Nspire there is a factor command which comes to the rescue.

The question of why divisibility rules work is a fruitful exploration for students. For more on proving divisibility rules, see the resources below.

In my search for multiples of 7, I have a new place to look: license plates. In Connecticut, they recently converted the license plate format to two letters followed by five numbers, such as AB-12345. I can check these 5-digit numbers for divisibility by 7 while stopped at a traffic light.

Which leads me to the question of license plate formats and the Fundamental Counting Principle. Connecticut used to have license plates with three numbers followed by three letters: 123-ABC. When those ran out, they briefly used a format with one number, four letters, and finally one number, such as 1ABCD2, at first without a hyphen and later with one inserted after the third character, like 1AG-HJ2. I disliked those plates because they were hard to remember (a 3-character chunk is more memorable to me if it is all letters or all numbers). Thankfully, the new seven-character plates appeared last year even though the sequence hadn’t been exhausted.

How many possible license plates are generated by each of the designs? Multiply the number of ways to select each character to determine the total:

Old style:         123-ABC:        10*10*10*26*26*26

Interim style:   1ABCD2:         10*26*26*26*26*10

New style:       AB-12345        26*26*10*10*10*10*10

The interim style, with 45.7 million plates, has 2.6 times as many plates as the old style.  The new style has 67.6 million possible plates which is about 3.8 times as many plates as the old style.  And with a one-in-seven probability that the number is divisible by 7, there will be about 9,657,143 multiples of seven out there.

Now that’s a lot of license plates! In the meantime, I’m looking forward to the next great date coming soon: 4/9/16.  Not only is it a progression of perfect squares (when will that happen again?) but 492016 is a multiple of 7.

NOTES & RESOURCES:

For more on why divisibility rules work, see the following:

1. Math Forum: Explaining the Divisibility Rules [link]
2. James Tanton: Divisibility Rules Galore! [link]

For more about using fingers to multiply and why the tricks work, see Kolpas, Sidney J., “Let Your Fingers Do the Multiplying”, Mathematics Teacher, 95(4), April 2002.

New resource: (Updated 10/2017) I just came across this problem-based lesson on license plates by John Rowe, using license plates from Australia and the US.  Check it out here.