# Tag Archives: mathematics education

## Questions about an enVisionMATH worksheet (part 2)

Here’s another question about the same enVisionMATH worksheet we first met yesterday. Take a look at this section, and think about the mental processes you’d use to answer each of these problems:

Got it? Now, let me zoom out a little and show you a part of the worksheet you didn’t see before:

If you’re late to the party and don’t know what’s meant by “near doubles” and the arithmetic rules that enVisionMATH attaches to near doubles, read this post first. Questions:

• Now that you know that these are supposed to be exercises about near doubles, does that change the mental processes you selected earlier for working the problems?
• Should it?

Filed under Early education, Education, enVisionMATH, Math, Teaching

## Partying like it’s 1995

Yesterday at the ASEE conference, I attended mostly sessions run by the Liberal Education Division. Today I gravitated toward the Mathematics Division, which is sort of an MAA-within-the-ASEE. In fact, I recognized several faces from past MAA meetings. I would like to say that the outcome of attending these talks has been all positive. Unfortunately it’s not. I should probably explain.

The general impression from the talks I attended is that the discussions, arguments, and crises that the engineering math community is dealing with are exactly the ones that the college mathematics community in general, and the MAA in particular, were having — in 1995. Back then, mathematics instructors were asking questions such as:

• Now that there’s relatively inexpensive technology that will do things like plot graphs and take derivatives, what are we supposed to teach now?
• Won’t all that technology make our students dumb?
• Won’t the calculus reform movement dumb down our curricula with all this nonsense about graphs and multiple representations and so on?
• How can you seriously call a person a mathematician/engineer if they can’t [insert calculation here] by hand? What if they are in a situation where they don’t have access to technology?

And yet, I actually heard all of these questions almost verbatim from mathematics and engineering professors this morning, multiple times. (To the great credit of the speaker who was asked the last question, he replied: If an engineer is ever in a situation where he is without access even to a calculator, we have a lot bigger problems on our hands than just bad education. TRUTH.)  I was having serious third-year-of-grad-school flashbacks.

These questions aren’t bad; they’re moot. In 1995, mathematical technology was just at the level of expense, accessibility, and functionality that these questions needed to be dealt with. Students could conceivably purchase calculators for a couple hundred dollars that were small enough to slip into a backpack and could calculate $\int \ln(\cos x) \, dx$ symbolically. Should we ban the technology, embrace it, regulate it, or what? Should we change what and how we teach? The technology could be controlled, so the question was whether we should, and to what extent, and these were important questions at the time.

But that was 1995. What the TI-92 could do in 1995 can now be done in 2010 using Wolfram|Alpha at no expense, using any device with an internet connection, and with functionality that is already vast and expands every other week. (This says nothing about W|A’s use of natural language input.) The technology is all around us; students are using it; there is no argument against expense, accessibility, or functionality that can reasonably be made. It’s going to affect what our students do and how they accept what we present to them regardless of what we think about it.  So I’d suggest that questions such as What do students need to know how to do in an engineering calculus course? and How do we ensure they can do those things? are better questions for now (and might even have been better then).

Some of the conceptions of innovative teaching and learning strategies I saw also seemed stuck in 1995. I won’t name names or give specific descriptions in order not to offend people who probably simply don’t know the full scope of what’s gone on in mathematics education in the last 15 years. (Although I must call out the one talk that highlighted the use of MS Excel, and claimed that there were no other tools available for hands-on work in mathematics. Augh! You should know better than that!)

I will simply say that people who concern themselves with the mathematical preparation of engineers simply must look around them and get up to speed with what is happening in technology, in the cultures and lives of our students, and in what we know now about student learning that we didn’t know then. Read some seminal MAA articles about active learning. Talk to other people. Read some blogs. Something! We can’t stay stuck in time forever.

## The Illini method for simplifying a radical

One of my linear algebra students is an education major doing student teaching. Today he showed me this method of simplifying radicals which he learned from his supervising teacher. Apparently it’s called the “Illini method”. Googling this term returns nothing math-related, so I think that term was probably invented by his supervisor, who went to college in Illinois.

The procedure goes as follows. Start with a radical to simplify, say $\sqrt{50}$. Look under the radical and find a prime that divides it, say 5. Then form a two-column array with the original radical in the top-left, the divisor prime in the adjacent row in the right column, and the result you get from dividing the radicand by that prime number in the left column below the radical. In this case, it’s:

$\begin{array}{r|r} \sqrt{50} & 5 \\ 10 & \end{array}$

Now look for a prime that divides the lower-left term, say another 5. Again, put the dividing prime across from the dividend, and the quotient below the dividend. With our example, the array at this stage looks like:

$\begin{array}{r|r} \sqrt{50} & 5 \\ 10 & 5 \\ 2 & \end{array}$

In general, continue this process of dividing prime numbers into the lower-left entry in the array, writing the prime across from that entry, and writing the quotient beneath that entry, until you end up with a 1 in the lower-left entry. So the final state of our example would be:

$\begin{array}{r|r} \sqrt{50} & 5 \\ 10 & 5 \\ 2 & 2 \\ 1 & \end{array}$

Now, look at the left-hand column of the array. Group off any pairs of numbers you see. Multiply together all numbers which are representative of a pair. In our case, there is only one such pair, a pair of 5’s. Any numbers that occur singly are placed under a radical and multiplied. In our case, that’s the single 2. Then multiply the product of numbers which are in pairs times the radical which contains the singleton numbers. So we end up in our example with $5 \sqrt{2}$.

Here’s another example with a larger number, $\sqrt{2112}$:

$\begin{array}{r|r} \sqrt{2112} & 2 \\ 1056 & 2 \\ 528 & 2 \\ 264 & 2 \\ 132 & 2 \\ 66 & 2 \\ 33 & 3 \\ 11 & 11 \\ 1 & \end{array}$

There are three groups of 2’s, so outside the final radical we’ll put $2 \cdot 2 \cdot 2 = 8$. And the 3 and 11 are by themselves, so under the radical we put 33. Hence $\sqrt{2112} = 8 \sqrt{33}$.

Pretty clearly, all this method is doing is presenting a different way to do the bookkeeping for doing the prime factorization of the number under the radical. The final step of grouping off the prime pairs and leaving the un-paired primes under the radical is analogous to finding all the squared primes in the prime factorization.

This method is nice and systematic, and I can see why students (and student-teachers) might like it. But it seems to be obscuring some important concepts that students ought to know. With the method of factoring, looking for squared primes, and then removing them from the square root, at least you are dealing directly with the inverse relationship between squares and square roots. The Illini method, on the other hand, uses an approach of “put this here and then put that over there” with minimal contact with actual math. It does work, and it does keep things in order. But do students really understand why it works?

Your thoughts?  What does this method make clearer, and what does it obscure? Should high school algebra teachers be teaching it?

Filed under Education, High school, Math, Teaching

Here’s a problem I have with the way most calculus textbooks are written, and therefore by default the way most calculus courses end up being taught. Tell me if I am crazy or missing something.

We teach calculus from a depth-first viewpoint. That means that whenever we encounter a concept, we go as deeply as possible in that concept before moving on to the next one. There are some subjects where this makes sense, but in calculus we have a small number of main ideas that are made out of several concepts, and if we stop to attain maximal depth on every single thing, there’s a good chance that we never arrive at the main idea with any degree of understanding.

The big ideas of calculus — the rate of change (derivative) and accumulated change (integral) — are actually really simple if you consider them simply for what they are and what they were invented to do. Derivatives, for instance: You have a function, and it is changing in all kinds of ill-behaved ways. The object is to find out exactly how quickly it is changing at a given point. We quantify that rate of change by sticking a tangent line on the graph of the function at that point and measuring its slope. Really, that’s it. Slopes of lines. The rest are technical details on how to calculate this slope with some degree of accuracy, and those details range from graphical estimation to interpolation tricks to algebraic techniques.

But in Stewart’s Calculus book, the coin of the realm of calculus texts, here’s what students have to study before the derivative is defined: an entire chapter of precalculus review (a mind-numbing section 1.1 on functions and notation, mathematical models, families of functions, exponential functions, inverse functions and logarithms), then a chapter on limits in which students have to master finding limits from graphs, calculating limits using the Limit Laws, the epsilon-delta definition of a limit (mostly untaught these days), continuity, and limits at infinity.

Then there’s a section on “Tangents, Velocities, and Other Rates of Change” followed by two sections on the Derivative.*

This approach plays directly in to the greatest weakness of the average calculus student, which is algebra/precalculus content mastery and the ability to master technical details of calculations and theory. How likely is it, for the student who struggles to read mathematics or use algebra correctly, that this student will be in any shape to learn what a derivative is, and what one is for, by the time they get there?

You want students to master those technical calculations and theory, of course. But you also want those to be mastered in context, not just as mathematical tricks to be learned as parlor games. The few students who survive the onslaught of detail mastery and are still psychologically around to learn what a derivative is, often find it extremely hard to know what f'(3) = 2 actually means. All they know is that you bring the power down and subtract one, and maybe the Product Rule.

I’d prefer some kind of approach to calculus that is not depth-first but more like breadth-first, where students get a good grounding in the overall ideas of calculus and do some basic work before mining into the really deep details. Not all students really need those deep details, after all.

* OK, there is a section (2.1) where the ideas of tangent lines and velocities are briefly introduced. And then summarily ignored until the end of that chapter. The students typically ignore that material right along with the book.

Filed under Calculus, Math, Teaching

## Retrospective: Characteristics of upper-level math success (11.01.2006)

Editorial: This is installment #5 in retrospective week. When I announced retrospective week, I said that some of the articles I would be highlighting may not have gotten many comments but started larger conversations — and this is certainly one of them, although the conversation went totally to places I didn’t want it to go.

Read the article for yourself, and you’ll see that it is a reflection on what makes a successful student in an upper-level math course, what education programs often cite as characteristics of successful teachers, how those two sets are often portrayed as mutually exclusive, and why math education majors have to work to possess both sets of characteristics as an integrated whole in order to become great teachers.

But that’s not how a lot of readers took it. In particular, some of the education majors at my college read this article and took it to be a public put-down of their intelligence. There were even some people, for all I know not connected to my college at all, who anonymously sent messages to the dean and president of my college to complain about me and my negativity towards education majors. Without revealing details, I’ll just say that it all culminated in my quitting the blog for five weeks

Despite the controversy this article caused, and may cause again by re-posting it, I stand by my statements. Students have got to learn to be tough-minded, self-confident, and detail-oriented to succeed in upper level math courses; and they have to work at integrating this with being caring, compassionate people in order to be excellent teachers. Kids in school — my kids — deserve nothing less than excellent mathematicians who are excellent teachers. And for goodness’ sake, if you don’t agree with this, LEAVE A STINKING COMMENT rather than go running to the dean.

Characteristics of upper-level math success

Originally posted: November 1, 2006