## Dan Goldner Thursday, Mar 31 2011

This is a shout out.

Dan Goldner came on my screen last summer during Riley’s soft skills conference. My impression was that he was a bright-eyed bushy-tailed newbie (just off the student teaching year) with a surprising amount of classroom insight considering this.

At the end of the summer I met him IRL in a miscellaneously awesome context and have been following his blog Work in Pencil since then. In the fall of his first full-time year in the classroom, he didn’t produce a lot of content. (No surprise.) 2 posts in the early fall, 2 right before Christmas, then nothing for months. (I guess I’m not one to talk.)

But now he’s back, and I feel that my initial impression last summer, while quite positive, was actually an underestimate. I didn’t anticipate all this maturity. I want to let you read for yourself, so I’m going to minimize the endorsement verbiage. I will say this: disconcerting forthrightness and vulnerability combined with some real writing craft. Keep your eye on this one.

These two are my favorites. Go read now.

## Angle Sum Formulas: Request for Ideas Friday, Mar 18 2011

One of the student teachers I supervise is planning a lesson introducing the sine and cosine angle sum formulas. I wanted to give him some advice on how to make the lesson better – in particular, along the axes of motivation and justification – and realized that, never having taught precalculus, I barely had any! Especially re: justification. I basically understand these formulas as corollaries of the geometry of multiplication of complex numbers.[1] I have seen elementary proofs, but I remember them as feeling complicated and not that illuminating.

So: how do you teach the trig angle sum formulas? And in particular:

* How do you make them seem needed? (I offered my young acolyte the idea of asking the kids to find sin 30, sin 45, sin 60, sin 75 and sin 90 – with the intention of having them be slightly bothered by the fact that they can do all but sin 75.)

* Do you state the formulas or do you set something up to have the kids conjecture them? If the latter, how do you do it? How does it fly?

* How do you justify them? Do you do a rigorous derivation? Do you do something to make them seem intuitively reasonable? What do you do and how does it fly?

* Do you do them before or after complex numbers, and do you connect the two? If so, how do you do it and how does it fly?

Any thoughts would be much appreciated.

Thanks to John Abreu, who sent me the following in an email –

Please find attached a Word document with the proofs of the trig angle sum formulas. After opening the document you’ll see a sequence of 14 figures, the conclusions are obtained comparing the two of them in yellow. Also, I left the document in “crude” format so it’ll be easier for you to decide the format before posting.

I must say that the proofs/method is not mine, but I can’t remember where I learned them.

with an attachment containing the following figures (click to enlarge / for slideshow) –

As far as I can tell, the proof is valid for any pair of angles with an acute sum.

Notes:

[1]Let $z_1,z_2$ be two complex numbers on the unit circle, at angles $\theta_1,\theta_2$ from the positive real axis. Then $z_1=\cos{\theta_1}+\imath\sin{\theta_1}$ and $z_2=\cos{\theta_2}+\imath\sin{\theta_2}$, so by sheer algebra, $z_1z_2=(\cos{\theta_1}\cos{\theta_2}-\sin{\theta_1}\sin{\theta_2})+\imath(\cos{\theta_1}\sin{\theta_2}+\sin{\theta_1}\cos{\theta_2})$. On the other hand, the awesome thing about multiplication of complex numbers is that the angles add – the product $z_1z_2$ will be at an angle of $\theta_1+\theta_2$ from the positive real axis; thus it is equal to $\cos{(\theta_1+\theta_2)} + \imath\sin{(\theta_1+\theta_2)}$. This is QED for both formulas if you believe me about the awesome thing. Of course it usually gets proven the other way – first the trig formulas, then use this to prove angles add when you multiply. But I think of the fact about multiplication of complex numbers as more essential and fundamental, and the sum formulas as byproducts.

## Two More Links I Gotta Share… Sunday, Mar 13 2011

From the NYT, on value added – profiling a young, energetic and by all accounts highly successful teacher with a bad value added score.

I guess it was a matter of time before the media stopped acting 100% in love with value added scores; but what a relief.

I had a conversation with an old friend today who works in the federal government, in the department of labor. We were talking about various unhealthy, ineffective patterns and dynamics (and people, truth be told) in our respective professional worlds. Both of us are depressed by lack of effectiveness.

It is in the name of effectiveness, of course, that districts across the nation have been jumping headlong into the practice of rating teachers based on an opaque calculation with their students’ test scores, on tests that were already dubious measures of anything worthwhile, and then using these ratings to make decisions affecting teachers’ jobs. I don’t know the best policy environment to promote teacher effectiveness, but I know for certain it’s not this. If you want to find a perfect system for diverting all teachers’ attention away from their students’ learning and their own growth, look no further than value added ratings.

I don’t want to be preaching to the choir here (although I probably am), so to the proponents of value-added measures, let me say this:

I know what I’m saying sounds counterintuitive to you – why wouldn’t incentivizing having your students perform well on measures of their learning lead you to focus on their learning? I will put aside for the moment the extremely important question of whether state tests are a measure of students’ learning (let alone whether value-added methodology really measures teachers’ contribution to it), and respond with an even more fundamental question:

Think of the last time you did something complicated and nuanced, something rich and interesting enough to require some creativity and artfulness from you. Imagine now that you were REALLY ANXIOUS about the outcome while you planned and performed your work. Would this anxiety really help you do it better?

* * * * *

On a lighter note (well, sort of):

From Shawn Cornally, on teaching evolution:

So many people trying to tell us how to teach promote the just-say-it-better model of education. This doesn’t work. You can’t just talk at kids and say things ‘better’ than your teachers did. They need time to simmer. They need time to think. They need people to lay off and let them fucking think for a second.

Word.

## Still Here, Still Learning Friday, Mar 11 2011

I last posted in October. I wrote a review of Waiting for Superman that generated more traffic than I’d ever seen before on this blog. Since I had been intending to continue my series on the idea of mathematical talent since the summer, I decided not to post again until I was done with the next installment of that series. But because it involves some research, and I care about it a lot and want to get it just right and tend to get kind of obsessive about things like that, and because there’s been a lot of other stuff going on so I haven’t been working on it consistently, this has kept me from posting anything at all for 4.5 months. So maybe it was time to revisit that agreement with myself?

And a few days ago, JD2718 wrote me an email to the effect of, “yo, what happened to you?”

So, here’s a partial answer –

a) I learned a lot about leadership. One of my jobs this year has been to facilitate the weekly math department meeting at a high school, and plan the agenda for this meeting. This has gotten me involved with the communication channel between the department and the principal. I feel really grateful to have had the opportunity to do this. It has caused me to start to develop a completely different skill set than I’ve ever had to use before. (To give you a whiff of what I mean, it inspired the following facebook status: “Ben Blum-Smith thinks it is important to be a straight-shooter and a diplomat, and that you do each better by doing the other one.”)

b) I learned a lot about training new teachers. Another of my jobs this year has been as a faculty member of an MAT program. In the fall, my colleague Japheth Wood and I taught a “math teaching 101” typed course for our cohort of 12 preservice folks; this winter we taught the “math teaching 102” installment. They’ve been in apprenticeships for 9 weeks and we’ve just gone through observing them actually teach a few times, so now on my mind is – what am I happy with in their teaching? What’s missing? And what implications does all that have for our fall and winter courses?

c) I’ve continued to design and implement a graduate course on algebra and analysis for the faculty of a high school. This has been both awesome and very challenging. We chose to organize the course to culminate with the Fundamental Theorem of Algebra. At the beginning of the year I thought this was a reasonable goal and the course would not feel hurried. Now, 2/3 of the way in, somehow I’ve found myself feeling pressure to go through significant chunks of material at breakneck speed. That tension is of course absolutely part of the lives of all the participants in their own classrooms, so in a way it’s cool that this is parallel; but still. I am implicitly making a case with this course for the principles of math teaching I believe in, so I’d better be living those principles in my teaching of it. A few of them I feel like I’ve been 100% consistent with:

* Every day I will bring you questions that are worth your time, questions that even I think are exciting to think about even though I already know the content.
* A math course should have a plot, with beginning, middle, end, dramatic tension, resolution. (Math teaching as storytelling.)
* Central to learning math is the interplay between formal/rigorous thoughts, definitions etc. and intuitive notions. I will always stress the connections between the two.

Other principles I feel like I’ve nailed some of the time and totally let slip away other times in my concern to make sure we get to the content:

* (Closely related) The most powerful certification of new knowledge is consensus of the learning community, the same way new knowledge is certified in the research community.

3 classes ago I had them prove the irrationality of $\sqrt{2}$, spent the whole period on it, left them all the heavy lifting, noticed and brought out points that were bothering people, and generally aced these last two principles. The last two classes have felt the opposite way. I think I was talking 80% of the time in the most recent class. Lots of questions never got answered because they never got aired; lots of productive thoughts never got formed because they never had time to. Anyway, getting this course right will continue to be an engaging challenge.

d) I applied to doctoral programs in math. Now I need to decide where to go. The choices are NYU, CUNY and Rutgers. I feel very excited and torn.

e) If anybody remembers the ellipse problem that Sam Shah brought back from PCMI, and which I wrote about back in August… Japheth and I have completely solved it. I am going to tease you with this tidbit and not the solution itself because we wrote a manuscript on it which we hope to get published.

f) Okay this doesn’t fit under the rubric of “what happened to me” but here are some links you might enjoy:

* A Teacher Story by Anna Mudd. Anna’s blog, Drawmedy, is a beautiful kind of writing which I won’t try to describe. It’s not an education-themed blog so I was delighted to see her take on her experience as a teacher.

* This gem from Vi Hart: Wind and Mr. Ug

* Taylor Mali’s What Teachers Make. This poem is definitely amazing, and if you’ve never seen it, I think you won’t be sorry if you watch it before reading the next sentence. <pause>Pause while you watch the video.</pause> It brings up some ambivalent feelings in me too – these are a story for another time, but here’s the short version: It’s related to the tone of the current national conversation about education, which is all about how the incompetent slovenly dumb*sses in front of our children are f*cking everything up. In this context, Mali’s piece is an eloquent testament to the value of our work, but it also makes me uncomfortable. Mali appears to have been amazingly happy with the job he was doing as a teacher when he wrote and performed this. But I don’t think that (especially in light of the current climate of the conversation) feeling like you’re doing an amazing job should be in any way a requirement for testifying to the value of your work; especially since most of us do not feel that way, most of the time.

* Speaking of the current national conversation about education, a new study by the National Education Policy Center came out on New York City’s charter schools, which are often touted as models for the nation.

* It’s weird to experience yourself as an unwitting participant in a historical zeitgeisty trend, but I do. I have the strong feeling that the traditional distance between the mathematics education community and the mathematics research community is closing, and I, a classroom teacher and teacher trainer entering into a math PhD program, am like completely an example of that. Another is the latest issue of the Notices of the American Mathematical Society, which is the research community’s professional association. It is devoted to education. You can download it for free.

(Thanks, JD2718, for making me write all this.)