News: Thoughts about maths thinking
Obscuring the GST by making it simple
I was helping out at Roseworthy Campus yesterday as the Vet Medicine students were learning about budgeting for a Vet Clinic as a business. One aspect of this was calculating the amount of the cost of goods and services that was GST (stands for "Goods and Services Tax" – in other countries it's known as VAT or Sales Tax). The Excel sheet they were working in already had the formula worked in and it was this: GST = (Total Price)/11.
There is only one kind of function that distributes over plus
There is a very common thing that students do that causes pain, distress, confusion and depression in any maths educator who witnesses it. Both the error itself and the educator's response to it are very clearly described by this excellent picture from the blog "Math with Bad Drawings":
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The square root of two
In first year maths, they briefly study the five families of number: the natural numbers N, the integers Z, the rational numbers Q, the real numbers R, and the complex numbers C. In particular, they focus on the distinction between the rational numbers and the real numbers. A classic proof they are given at this time is one that the number √2 is irrational. This blog post is about some alternative proofs.
Inspiration, not instructions
We have a big on the MLC wall that gives students advice for solving problems. One of those pieces of advice is that to decide what to do for your current problem, you could look at other problems for inspiration. Yesterday I saw the dangerous results of what happens if you look at other problems for instructions rather than inspiration.
Complex is not the same as complicated
The Complex Numbers are unfortunately named. Most people take the word complex to mean "difficult to understand", so the very name we give this family of numbers sets students up to think it's going to be a lot of hard work to understand them. This is sad, because they really are very very cool and not quite as difficult as people make them out to be.
The advent calendar function
In a previous post I discussed how we need ways to think about functions that are not curves on an x-y-plane. Well I have a seasonally-appropriate one for you: the Advent Calendar.
A function is not a graph
When students learn about functions at school, we spend a lot of time forging the connection between functions and graphs. We plot individual points, and we find x-intercepts and y-intercepts. We use graphing software to investigate what the coefficients do to the graph, and discuss shifting along the x-axis and y-axis. We make reference to the graph to define derivatives and integrals. Some teachers help students to recognise from the formula of a function what general shape its graph ought to have, such as recognising that a quadratic function must have a parabola-shaped graph. (I wish this last point was much more strongly pushed, actually.)
Rotation confusion
I had a long chat with one of the students the other day about rotation matrices. They had come up in the Engineering Physics course called Dynamics as a way of finding the components of vectors relative to rotated axes. He had some notes scrawled on a piece of paper from one of my MLC tutors, which regrettably were not actually correct for his situation. I know precisely why this happened: rotation matrices are used in both Dynamics and Maths 1B, but they are used in different ways (in fact, there are two different uses just within Maths 1B!). It's high time I made an attempt to clear up this confusion, especially since three more students have asked me about this very issue in the last week!
Contrapositive grammar
We had students the other day from Maths for Information Technology and their task was to form the contrapositive of a several statements. Given a particular statement of the form "If A, then B", the contrapositive is "If not B, then not A", so mathematically the problem is not actually very difficult. However grammatically the problem is much harder than it looks.
Too much time on his hands
On the train a while ago I overhead some people talking about Heston (the celebrity chef). Apparently he had been doing a series on giant food. It involves him trying to figure out the physics and logistics of trying to produce food on a giant scale – for example, a three-metre tall soft-serve ice-cream cone.
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