The Best of the Math Teacher Blogs 2015

It’s never been easier to miss a great math blog post. The MathTwitterBlogoSphere –– known as #MTBoS around social media –– was once a small group of math teachers willing to make themselves vulnerable, putting their practice online. As the community has expanded, even the most dedicated readers struggle to keep up with the deluge of thoughtful commentary, engaging and interesting tasks, and stories that we can all learn from.

To help keep you from missing out, we have compiled some favorite posts from this past year, as nominated by #MTBoS folks on Twitter, into a book. These posts are as rich and varied as the educators who wrote them. Some delve into specific content. Some tell stories of change and growth. Others explore teaching practices, new or well established. We hope that you find some that provoke and push you, and others that make you smile. Most of all, we hope you make some new connections in the MTBoS community.

This book has another purpose as well. Since 2012, folks from the MTBoS have participated in an annual “tweet up,” a two-day math extravaganza called Twitter Math Camp (TMC). Unlike regular conferences, teachers come knowing who they want to meet. They come to continue conversations that have been taking place online, through blogs and twitter. TMC is a rich and personal learning environment. The grassroots nature of TMC means it is lively, personal, tailor-made, and unpredictable. However, most teachers have to pay their own way. We will use the money raised through sales of this book to start a fund to bring along some of the teachers who would not otherwise be able to participate. We think that TMC is a unique professional learning experience, and we hope to share it while we grow our community.

The book is nearly ready for publication, but we need assistance with a few tasks (we’d like to add an index and list embedded links at the bottom of each post so they’re accessible to anyone reading a paper copy). If you’re interested in assisting please email Tina (tina.cardone1 on gmail) and she’ll get you set up with a task.

Thank you for reading, and thank you for your support.

— Lani Horn & Tina Cardone
P.S. Sorry that we were super secret on this project! We didn’t decide to do this until after the #MTBoS2015 conversation started. We were so impressed by the quality of the nominated posts, it seemed like a great opportunity to do something for this amazing community. As long as we are confessing, we also didn’t announce it until now because we weren’t sure we’d be able to finish it! If people like the idea then we’ll have a more public and organized process for 2016.

Laying the Groundwork for Logarithms

s

Strangely, I have had occasion to do a few tutoring sessions with different kids recently around exponential and logarithmic functions.

This particular mistake set off a few alarm bells:

logblog

 

Do you see what the student is doing here? She is treating

log a

like a variable that is being divided instead of a function.

I looked at the student’s notes, and all the usual log laws were there. But she did not yet have the unshakable understanding that logs are functions. I realized that there are some foundational ideas that she needed before we could really make sense of all of this.

Here are a couple of essential ideas I want to communicate to students about logarithm functions.

First, functions can be described as actions, so I always make students explain what a function is doing.

The question you should ask about every function is: what are we doing to the input to get to the output? I call it “saying the function in English.”

Since we usually teach logarithms after exponential functions, let me start with them.

I ask, What do exponential functions do? They provide rules based on repeated multiplication. So the function

2x

tells us that “some number (y) equals 2 multiplied by itself any number of (x)  times” to get y. We can do this with different examples, talk about how the function grows, look at the graph, look at tables, compare the growth of exponential functions to linear and quadratic ones. My goal is to get kids to have a feel for what is happening with exponential growth so well that when somebody says, “It was growing exponentially!” they can decide whether that is an accurate statement or not.

This is the first part of the groundwork for understanding logarithms.

Second, remember that anything we do in mathematics, we always find ways to undo.

This is thematic in all of mathematics. It becomes a chant when I teach math.
I say to students:
“Since this is math, anything we learn to do, we need to ….?”
They soon learn to respond with:
UNDO!!!”

Doing-and-undoing is a good mathematical habit of mind to emphasize, because students start to anticipate that when we learn some new funky function or operation, an inverse is coming down the pike. They are not at all surprised to learn that trig functions have an inverse and so on.

In this case, since we have learned to exponentiate, they can guess we need to un-exponentiate.

shrug

That’s just how math works!

I like to show inverses of functions in all of the representations. The idea is the same in tables, graphs and equations: the x’s and y’s switch places.

For tables and graphs, it’s fairly easy for students to figure it out. But the algebra gets tricky. To find the inverse of the previous exponential, for example, we need to derive it from:

inverse 1

This immediately creates a mathematical need to “un-exponentiate.”

So when we want to solve that equation for y, let’s undo exponentiation with a function we call a logarithm. Logarithms undo exponentiation.

logging the inverse
Since the log undoes the exponentiation, we end up isolating the y.

this one!

I also tell them we read this as “log base two of x equals y.”

So when you see an equation like:

fixed

you are asking “2 to what power equals 8?” I have them practice explaining what different equations mean.

Now your students are ready to learn all the details of working with logs!

Tell me your ideas in the comments.

[Before I close, vaguely related Arrested Development reference:

bob loblaw

Because this is a log law blog. But I guess I don’t really want to talk about log laws. Anyways…]