# How to make Calculus II seem motivated, interesting, and useful?

I am due to teach Calculus II in the fall at an American state university. Our calculus sequence is somewhat slow, due to the fact that many of our students come with limited backgrounds. Most of our typical syllabus consists of the following.

1. Techniques of integration. We teach the students to memorize and apply complicated techniques for evaluating obscure integrals --- all of which Wolfram Alpha can do in a fraction of a second.

Why do they work? Well, that requires a lot of mathematical maturity to understand, and for the most part we don't even try. For example, Stewart's calculus book makes no attempt to explain why partial fractions work, not even a handwavy one. Just "A theorem in algebra guarantees that it is always possible to do this," and the rules are presented for memorization, in all of their complicated glory.

2. Sequences and series. This chapter is a huge, long slog in every calculus book I've ever seen. Stewart's book starts with lots of scary theorems ("Every bounded monotonic sequence is convergent", proved with epsilon-delta), so that by the time you write $1 + \frac{1}{2} + \frac{1}{4} + \cdots = 2$ on the board, or even $.9999\dots = 1$, the students are made to feel that it secretly means something complicated and technical which they half-admit they don't really understand.

From there it gets even worse. Typical problem in Stewart: Does $\sum_{n = 1}^{\infty} \frac{n + 5}{\sqrt[3]{n^7 + n^2}}$ converge or diverge? Well, there is a rule for that -- one of very many -- and for the comparison and integral tests you can at least give a fairly convincing simple explanation for why they work. But I shudder to ponder how many of our students understand that the Latin word converge means equals a number -- this fact is obscured because usually there is no good way to evaluate what this number is.

In the meantime -- where do these series come from? The students will have seen few or none, and typically applications are de-emphasized in the book (and also feel a bit artificial or canned). The textbook does not provide the material with which to convince the student that such a series is a natural thing to write down, except if one is looking for convenient fodder for homework or an exam.

Now, I could revise the material to do it "my way", but if I really did it my way, I'd end up teaching something radically different from your average Calculus II course. (And my department expects me to stay fairly close to the book.)

I'm feeling unprepared to make the case to my students that this course is interesting, useful, or important. What can be done with this material?

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There is a genuine problem here. Such courses are most often "weeder" courses, and the kids know this, either explicitly or subliminally. E.g., they sense that they don't genuinely "need" the material (except to survive it to get to their chosen major...). The engineering and science majors know it is antique, etc. In particular, you would not want to find yourself defending the choices made for the syllabus, but neither would you want to criticize it. But, then, too, the kids' motivation to pay attention to "optional" stuff is severely compromised, and they may feel you are misallocating... –  paul garrett May 26 at 13:31
... class time which could better be spent helping them prepare to not get weeded out. Conclusion: enrichment additions to such a course have to be rather slight and in-passing, or the students may have a legitimate complaint. Long-range conclusion: such courses are archaic to the point of embarrassment, but it'd take considerable effort to update them. –  paul garrett May 26 at 13:33
–  J W May 26 at 18:56
–  J W May 26 at 20:15
Frank, speak to faculty in other departments that require the course to find out from the syllabus what topics they want their students to know and why. Or create an online survey with lists of topics and ask the faculty to mark those they consider important and allow them to submit written responses too as feedback. –  KCd May 27 at 11:59

## 7 Answers

While it doesn't motivate much of the dense and technical morass that is Calculus II, I've made it a little more fun (for me anyway) by thinking about the course as trying to understand the infinite. Our version of the course also has improper integrals (clearly about infinity) and power series (a polynomial of infinite degree).

I tend to drop in some facts about infinity throughout the semester.

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+1 Short + sweet! –  Gamma Function May 26 at 1:23
Came here to say the same thing that @ncr did -- the basic idea behind all the concepts in Calc 2 is infinity. That's why students can have such a tough time grasping the subject matter! So make it a course about infinity. And while you're at it, make sure the technical algebra doesn't take over -- cut back on some of the more mechanical integration techniques like some of the trig substitution. You won't miss them. –  Robert Talbert May 26 at 23:18
Hmm...I'd consider Calc 1 as a course that is all about understanding the infinite. Calc 2 is just more of the same. –  Ben Crowell May 29 at 19:43

Don't you also do volumes of rotation, and polar, parametric etc?

The volumes and work problems are the most down-to-earth problems in the course I teach.

And I end the infinite series unit with Maclaurin series, and their ability to make integrals of things like e^(-x^2) solvable, which has a solid connection with statistics.

In the techniques of integration unit, I have them do an area project, using Simpson's rule, so they get a sense of how messy real-life applications may be.

Definitely, try to help your students understand why each technique works.

I find Calc I much more satisfying, but I enjoyed Calc II this past semester. I am still searching for ways to make it work better for the students.

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"Every bounded monotonic sequence is convergent", proved with epsilon-delta

Snore. Seriously, that won't motivate anyone. But if you show me how it applies to real-world problems that I actually want to solve....

I took calculus in University and even got a surprisingly good mark in the class. The one and only thing I can recall is I should use 2πr for circumference - the professor (who was great, and Welsh. That's important here) would mark πd wrong. Why do I remember this point? This is the only thing covered that had applications outside of physics labs, where we used differentials to work out absolute error. In 1985 that was a pencil-grinding slog that crashed the calculator half the time, and no one really cared.

As you pointed out, Wolfram Alpha can do the grunt work instantly and produces pretty graphs. Skim over the mechanics (which I won't need any more than long division), connect input directly to output, and then explain why it works.

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What is wrong with $\pi d$?? –  Jp McCarthy May 26 at 12:10
@JpMcCarthy, everybody (but seemingly not Welsh people) knows that the only correct formula is $\tau r$... –  vonbrand May 26 at 12:43
"pie-dee", in Welsh, is apparently a rather substantial insult. I (much) later asked a Welsh co-worker what it meant, his reply was "Wot? 'Ew said that to ya? Good way to start a punch-up." –  paul May 26 at 14:15

I'd try to get more understanding than rote regurgitation of formulas out of them. As you note, there are computer algebra systems around (I'm a fan of maxima, it even runs on my cellphone) that can handle the routine effortlessly. It would be nice to have the same at hand for everybody, and as an open source one maxima fits that bill. Or insist on some web-based system, like Wolfram alpha.

Instead of having them compute nasty integrals by hand, let the CAS handle that. Do compute all sort of weird volumes of rotation and such, but get symbolic/numeric results (and ask for that in homework). Ask for the set up, and have them attach the commands and output of the CAS, and then state the result. In exams ask for how to set up the computation, how to use e.g. partial fractions on a sum or integral (not "give me the coefficients", but "to compute this, do you split ...").

For sequences and series, I'm afraid there isn't much that can be done. But freeing up time by leaving out the drudgery should help a lot.

Take care to coordinate with colleages working in parallel, check what exactly following courses require. In particular, if some CAS is standard there, or there are "student editions" available through the bookstore, use them.

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From my experience tutoring, what has worked is first presenting a real world problem that needs solved then show how Calculus can be used to solve it. Position Calculus as a tool that can solve real problems and show how to translate problems to math and back again. Math is the tool that makes Science possible. Science without math is simply observation!

It also helps to reinforce that math is exact and a chain of steps that has to be done correctly otherwise it only takes one break in the chain to miss a problem. Don't let one misunderstanding of one formula break the chain! Students have to memorize formulas and understand the steps exactly. It takes practice to perfect understanding; and patients with yourself to go through the perfection process.

I always say they are lucky as every problem presented in class has a correct answer, they just have to find it. Thinking a problem cannot be solved is simply not true, they just need to find the secret on how to solve it.

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The real problem is that the course has to serve the needs of math majors, engineering/physical science majors, and life science majors.

For math majors, 100% of the material in a traditional freshman calc course is relevant, and no apologies are required. It doesn't matter that computer algebra systems can do hard integrals; we need to keep on educating human beings who have the skills to write a computer algebra system. These students need to understand the foundations of the subject, which are nontrivial and took hundreds of years for the world's best minds to work out after the invention of the calculus by Newton and Leibniz. For example, people like Euler used to seriously manipulate series like $\sum_{n=0}^\infty (-1)^n n!$, because the notion of convergence wasn't obvious and hadn't been invented. Lagrange tried to build calculus on Taylor series as a foundation, in order to avoid limits and infinitesimals; people at that time didn't understand that not all functions were analytic. For a student who's a math major, the only serious problem with this type of course is that the curriculum typically ignores the rehabilitation of infinitesimals in the 20th century.

For physical science and engineering majors, series, especially Taylor series, are important, practical, easy to motivate, and will be used by them for the rest of their working lives. Methods of integration, on the other hand, are less likely to be useful, although there may be times in their upper-division coursework where their teachers will want to use these ideas without having to apologize, and in contexts, e.g., proofs of general facts, where a CAS isn't the right tool. For example, integration by parts is used in the standard derivation of the Euler-Lagrange equations of motion from the principle of least action; because this is being proved in general, not for some specific example, you need to understand integration by parts in order to understand the proof.

For nearly all life science majors the second semester of calculus is a ridiculous waste of time. It's required of them at some more selective schools because majors like biology are "impacted," so the biology department is looking for a way to weed students out.

There is no good reason why all students who take calculus should take the same two-semester freshman calc course. At the community college where I teach, we offer four different flavors of freshman physics. The math department could do the same. The most probable reason that freshman calc is one-size-fits-all is that other departments want it as a "weeder" course.

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I'm yet to come across a nasty integral in a proof where the "how to evaluate it" aspect i is more relevant than its value. Care to exemplify? –  vonbrand May 27 at 2:28
You've elevated Robinson pretty high among the many (e.g. Bishop, Conway, Lawvere) who refounded the calculus. I'm happy leaving all of them out: even for math majors, probabilities and partial derivatives and numerical computations are the serious omissions for me. –  Matt F. May 27 at 2:30
@vonbrand: I added a specific example. –  Ben Crowell May 27 at 16:40
@MattF.: Good point about singling out Robinson. Fixed. Math and engineering majors will learn partial derivatives in a vector calculus course, so I don't see the harm in omitting them from the second semester of a freshman survey. The trouble with pretending that NSA and SIA never happened is that we perpetuate a culture in which scientists and engineers universally use infinitesimals (as they've done for 300 years), but are not prepared properly by their freshman calc course to use them. Ignoring developments since 1965 also makes it harder for students to decode the Leibniz notation. –  Ben Crowell May 27 at 16:44
@Ben: Don't those scientists take a course in multivariate integration? Differential forms are the only "justification" the "fractional" techniques need. Just the FTC is enough. –  nomen May 27 at 20:16

Try using smooth infinitesimal analysis and point out that if we leave the powers of epsilon in we get finite difference calculus. Also look at this. It seems to me that limit theory only applies exactly to some early results of integral calculus (eg the quadrature of the hyperbola); and apart from that it's an approximation for which nilpotent infinitesimals are equivalent.

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Dear downvoter: counterargument please! –  mistermarko May 26 at 19:53
I'm not the downvoter here (at least not yet), but: How does smooth infinitesimal analysis fit with the constraint that "my department expects me to stay fairly close to the book"? –  Matt F. May 26 at 22:49
@mistermarko: Your suggestion that "limit theory only applies exactly to some early results of integral calculus" seems, at best, misleading. –  Pete L. Clark May 27 at 6:58