Tuesday, March 13, 2012

Exponential Functions: Folding and Shopping

I've never been all that happy with my presentation of exponential functions.  I usually slap a couple of functions on the board, plot some points with the class, and then write up a list of these functions' characteristics.  Boring.

Thankfully, I recently came across Sam Shah's method of exploring exponential functions using paper folding.  I like this idea so much more than plain old point-plotting (though I ask the students to do that as well).  Here's the worksheet I had my classes fill out before introducing the formal definition of an exponential function:

Paper Folding Exponential Functions



We spent 15-20 minutes on this worksheet in class before diving into the lecture.  That's a lot of time for a college class, and I felt rushed the rest of period, which is never good.  So, next semester I may assign it for homework the day before instead to save some time.  I would have to give some kind of hint as to how to find f(x) and g(x) though, because the students were a bit unsure of the pattern going on.  I don't think anyone got 2^x, but most did see that we were multiplying (or dividing) by two each time.

Once we got into the lecture part, I gave the students a great cheesy word problem:


One of my students noticed that it didn't take much time for the spending to increase significantly, which I was quite happy about.  "So the moral of the story," I began to say...

"Is not to be exponential when you're shopping!"  she finished for me. 

Perfectly said.

1 comment:

  1. For the academic session, SEBA has issued a revised condensed syllabus for Assam HSLC. The updated HSLC syllabus should be downloaded by students studying for the Assam 10th board exams. The Assam 10th syllabus is published by the Board of Secondary Education, SEBA Syllabus Assam (SEBA). Assam comprises the units and subjects that must be learned in order to prepare for the board test. The English, Mathematics, Science, and Hindi disciplines are all followed by SEBA.

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