Tag Archives: AP Calculus BC

Back in the Groove

Our school has a two-week spring break at a silly, early time in the year. We have been back for a week now and I feel like my students and I are all getting back in the groove again. I know that the dreaded senior slump will continue to pick up momentum but at least I am still seeing some energy and engagement from most of my seniors.

I have a few posts bubbling in my brain and I suspect it’ll be a busy blogging week. Tonight I want to briefly touch on my AP Calculus BC class. We are just settling in to our last major required topic of the year, the Taylor / Maclaurin polynomials. I wrote a little GeoGebra demo (you can find it here) and I started off by showing them (without revealing the mechanics behind the scenes) a polynomial approximation of increasing degree for the trig function y = cos x. We played a little noticing and wondering and saw that at certain stages the polynomial did not change. It did not take long to deduce that this happened at the odd powers of the Taylor polynomial. This led to one student remembering something about the symmetry of cosine, another student mentioning that this was a y-axis symmetry and, finally, a third student mentioning that this is even symmetry. So the lack of development due to the odd powers of the Taylor made a little sense. We then switched to y = sin x (as in the link above) and, unsurprisingly, saw that the even powers seemed to do little or nothing here. We did a little more noticing and wondering watching the Taylor expand on GeoGebra. I should note that all of this was centered at x = 0 (or, in the Taylor notation, we had a = 0) GeoGebra’s sliders allowed us to begin shifting that value and some interesting (and ugly/scary) things started happening to the Taylor equation. My kiddos quickly saw that the equation seemed to be undergoing a simple horizontal transformation – at least in the x terms. The coefficients were changing in some mysterious ways. Finally, we looked at the Taylor series for y = e^x. One of my students asked a great question at this point. He asked – Why are there all those factorials in the bottoms? I skipped this question around the room a bit to see if anyone wanted to make a guess. They quickly observed that exponents in the numerator were clearly attached to the factorials int he denominator but – understandably – they had no solid guesses. Without giving away all the mechanics (we have plenty of time for that) I asked what the derivative of x^7/7! is. I was told it would be 7x^6/7!   Correct for sure, but unsatisfying. I must have made my unsatisfied face because one of my students offered a much cleaner version of that answer as x^6/6!  Again, I did not go into the mechanics at this point, but there did seem to be some sense that this was an interesting thing to note. I was pleased by the power of the graphics of the GeoGebra applet. I know that I could do something similar in Desmos but I don’t know the commands there as well as I do in GeoGebra. I will start class off tomorrow with the power series we derived for e ^ x and I’ll ask for derivatives and integrals of that. Should be fun to see them realize in this format why the derivative of e^x is itself.

Fun to be back and excited to unfold Taylor’s series’ with my students. This was one of the genuinely awe inspiring topics when I studied Calculus. I remember being amazed by this idea and it’s mechanics. I hope I can share that wonder.

The Mysteries of Students’ Thinking Processes

A busy week of writing letters for advisees, writing a letter of rec for a former colleague, and pulling weekend dorm duty. Back on duty again tonight, so it is three out of four nights now!

Last week was the first time in quite a while that I found myself largely disappointed by my students and I have a couple of questions I want to air out. Trying to understand what students understand through assessment is, of course, one of our big challenges as teachers. People much smarter than I am have been hashing this out for a long, long time. So, I have two stories to share that are each nagging at me.

In AP Stats we are wrestling with probability. Most of my students have had very little, if any, exposure to probability before this class so this tends to be a tough unit. We had a problem on our last quiz that went like this:

Mr. Felps has 28 students in his AP Calculus BC class and 8 of them are left handed. We know that approximately 10% of the population is left handed. Can this situation in Mr. Felps’ class happen by chance?

A number of my students felt that this could not happen by chance. It seemed too unlikely to them. This bothered me a bit since we had looked at some simulations and talked about runs of short duration. We had discussed the law of large numbers and looked at a decent EXCEL simulation. I thought I had covered our bases on this one. But what really flustered me was that the follow up question asked for the probability of 8 out of 28 left handers under this condition. Every one of my students attempted this computation. Almost all got it right. BUT – a number who got it right had just told me that it was impossible for this to happen by chance. Somehow in the span of two minutes they seemed to forget that it was impossible and instead gave me the small percentage chance of it happening. What happens? Why do such good students have these kind of hiccups, especially in assessment situations? Man, it feels as if this is THE golden treasure to find as a teacher. How can we help our students step back and be metacognitive enough to sidestep these mistakes?

The second situation involves my Calc BC crew. We had a test last week and I try not to have too few questions on these tests so that each question does not feel so overwhelmingly significant. i have settled on feeling comfy with 7 questions in a 45 minute or 50 minute class test. Our recent unit on arc lengths and surface areas involve some problems that take a bit of time. To compensate for this while still having 7 questions I threw in what I thought was a gift wrapped set of points. Here is the question I tossed in as a softball for them.

I realize that if I increase my cycling speed by 3 MPH it will take me 40 seconds less time to cover each mile. What is my original speed?

I had students who left this problem completely blank. AP Calculus BC students who were so stymied by this that they did not even write an equation relating the information presented to them. I’ve been wrestling with this for days on a number of levels. It feels like this was an easy gift to them, one that my competent Alg II kids can easily solve. However, this was clearly not the way the problem was received by my students. They felt tricked or ambushed. They feel like it is unfair to lose points on a Calculus test on a problem that does not feel like it has anything to do with Calculus. I sort of sympathize on some level, but I feel that it is absolutely essential for these kids – kids who want to pursue serious, high powered technical degrees and futures – to be able to synthesize and recall old ideas with ease. Man, I am frustrated by this one. I felt I was tossing them a bone and it got stuck in their throats.

I have so much thinking to do (still!) about assessments and understanding what my kids understand.

Catching Up and Looking for Some Ideas

There are a few ideas/questions banging around in my brain. No school tomorrow here so I can relax a little more than usual on a Sunday night. I’ll try to be coherent and I hope to get some feedback here or through twitter (where I can be found as @mrdardy)

On Friday our school had the day off and we have been encouraged to use this as a professional development day by our administration. I chose to travel a few hours to visit a school where an old friend is working. The school does some interesting work in the STEM arena and they balance an IB program as well as AP expectations. I gathered some ideas that I will be bouncing off of my colleagues and administrators, but more importantly I just felt energized. I walked away excited to have made some new contacts, happy about many of the things we do at our school so well, interested in figuring out how to develop cultural pieces to support some ideas that work there, and filled with some ammo to talk about the need for schedule changes at my school. As a young teacher I never visited another school. I have long had the habit of visiting other classes at my school and I never feel like I do that enough. It has only been since I moved north 8 years ago that I started making the effort to visit other schools and I cannot recommend this enough. Where I live I pretty much have to drive two hours or so and I have done that the past two years. Every time I have reached out to another school I have received nothing but positive responses and a generous  expense of energy in making the visit happen. I also want to take this space and time to extend an invitation to anyone who wants to come and see our school in action.

On Thursday my AP Stats classes had a group quiz. I stood at the door with playing cards in my hand. Students took one (blind) from me and were randomly assigned to groups. Each class had four groups and each group had a different quiz. There was one question in common to all quizzes but otherwise they each had five different questions. It was SO much fun to listen in as they wrestled with these questions and as they explained ideas to each other. There were some healthy debates but it never got tense or unpleasant. Our school has a very international flavor and I was especially pleased to hear the voices of my international students in these conversations. So much of the material in this course is based on careful reading and vocabulary and I sometimes worry about whether this gets in the way of these students accurately showing me what they know. Have not graded them yet – that is tomorrow morning’s task – but I fully expect them to shine.

On Thursday my AP Calc BC class took a test on integration techniques. The last question on the test was this – Divide a pizza of 14 inch radius into three equal portions with two parallel lines. Most of my students wisely chose vertical lines. Two chose lines in the form y = mx + b, a bad choice. I went into this intending to give full credit even without a numerical value for the line equations. Setting up the integral appropriately is where the calculus is in my mind. Here is what I find myself wishing after this test and after looking at their work – I wish that they had access to desmos or geogebra while they were taking this test. I wish that they had something much more powerful than their TI calculators to visualize this, to try out ideas, to narrow down where the solution needs to be. I had to struggle through some ugly algebra and some calculus that should have been cleaner and more obvious. I’m impressed by the patience and perseverance I saw but I am frustrated since I know that better tools can help them work smarter on a problem like this one. How many of you out there have a setup where your students have access to these tools on assessments? Am I overthinking this by worrying about internet access during a test? Should I just trust that reasonably written questions can allow them to show me what they know and allow me to judge my students’ progress? I’m thinking hard about this and I would love some ideas.

Great Follow Up Day

On Friday I wrote about a pretty terrific conversation that came up at the end of our BC class. We had tackled a particularly gruesome integral – (tan x)^5 and I had done so by repeated patience substitution and I chose to let u = sec x and look for combinations of sec x tan x as the du piece. One of my students stayed after and showed me his work where he shoe u = tan x and du = (sec x)^2 He was frustrated and told me that he spent about a half an hour trying to figure out why his answer was ‘wrong’. So, I typed up my solution and had it on one side of a page. (This document and the graphs I created are all linked on my last post from Friday.) I typed up the solution my student arrived at and placed it on the back of the page. I had my students working in teams so they each had my solution and their classmates’ solution in front of them simultaneously. I asked them to examine each of them and explain why they did not agree. I heard some pretty good conversations, most of them simply concentrating on making sure that they even followed each of the solutions. We had talked about it on Friday so it was good to hear them reflecting clearly on that experience. After a couple of minutes, one of my students announced that he proved that both solutions worked. I played dumb and asked what he was talking about. He explained very calmly that since one answer was based on even powers of tangent and one was based on even powers of secant, we could show that they were nearly equal. They seemed to differ only by a constant. I then showed them the Desmos graph I created and the GeoGebra graph I created. Both programs were happy with my solution and with my student’s solution. Neither program was happy with the difference between them. But I showed them that every x input we could guess at in the difference function yielded either an undefined answer or an answer of -0.75

I used this conversation with a number of goals in mind. I want them to get in the habit of talking to each other. I want them to see that there is not just ONE way to do math problems – especially ones as sophisticated as the ones we talk about in BC Calculus. I want them to think about graphs. I want them to utilize resources such as Wolfram Alpha, GeoGebra, and Desmos. I want them to notice and wonder about relationships. They are not yet where I want them to be in these terms, but the more often I remind them and the more often I model this behavior, then the more likely they are to adopt these behaviors.

If I did not believe this, I might not have the energy to keep on keeping on in this job. But I do believe it and I do keep on keeping on.

Thank you world of math resources for my students! Thank you world of recourses for me!!