Blog Post

Graphing Calculator Issues

In my Finite Math class I have been heavily stressing the use of the graphing calculator, especially since the college requires the calculator for the course.  I would definitely show the students how to use the graphing calculator anyway, it’s just that since it’s required, I feel as if I have an extra obligation to make sure that the students are using the calculator that they spent their big bucks on.  Anyway, here are a few issues that I have run into so far this semester (and unfortunately, I ran into all of the issues on the same night so it totally looked like I didn’t know what I was doing):

Issue #1:  When using ‘Math Print’, the Radical Sign has a limit.

My calculator is the TI-84+, which has the operating system upgrade.  Of course my calculator was in the new ‘Math Print’ mode since that is the default.  If you know anything about this mode, you will know that the square root symbol shows up on the screen, instead of having to put parentheses around the radicand.  Well, guess what?  There’s a limit to how many characters can go under the radicand.  And the calculator doesn’t really indicate this until you’ve typed in all of the characters and then realize that the radical symbol isn’t covering the entire radicand.
I tried to calculate the radical anyway, despite realizing that the radical symbol wasn’t covering the entire radical.  And my answer was wrong, and I looked somewhat like a fool for giving an answer that was clearly incorrect.  So, please be wary of the lure of the new ‘Math Print’ mode.

Issue #2:  When graphing piecewise functions, compound inequalities can be tricky.

When I first got my textbook for this semester, I was quite excited because the book came with many resources, including a graphing calculator guide.  I printed the guide out immediately, and figured that I could refer to it as needed throughout the semester in case I forgot one of the commands.  I also figured that the guide would provide some tips and tricks to using the graphing calculator specifically for the textbook that I might not know about.  One of these things is graphing piecewise functions, as I have never done this in the calculator before this semester.
Before class, I thought I was prepared.  I practiced entering piecewise functions and I reviewed my guide.  However, once in class, I totally froze up when entering piecewise functions.  So, I referred to my guide, and the one thing I needed it for, it didn’t cover – entering the pesky compound inequalities.  I knew I had done it before and that there was something I just wasn’t remembering.  Well, good thing for me one of my students figured it out in a rare ‘aha’ moment.  Really, I don’t get those too much in my classes.  But this student is a really great student, so I gave her big props for figuring the fix out before I did.
Anyway, you may want to review this document if you ever intend on doing a live demo of piecewise functions in the classroom:

Issue #3:  Some graphing calculators display asymptotes (by default) and some don’t.

Someone told me about this issue last semester, but I really didn’t take it too seriously, since I figured that it was a technicality that I probably wouldn’t need to keep at the forefront of my mind.  Well, I was totally wrong about this, and totally taken off guard when during class, some students started getting different graphs.  Half an hour later or so after the students compared their screens and all made sure that they had entered the piecewise function correctly, I realized that the TI-83 and TI-84 calculators were displaying different answers.  Then about two minutes after that I was into another half an hour unplanned discussion about asymptotes.
It dawned on me on the spot, right then and there, that the TI-83 calculators display the asymptotes by default.  Of course!  That’s why the graphs look different.  Although, if I would have known how to at the time, I would have probably told the students with the TI-84 calculators to turn the asymptotes on so that everyone could see the same graph.  And here’s a post from the TI people on how to do that:
By Jon Oaks

College Math Instructor. Tech Enthusiast. Visionary. Creative Genius. But above all, I enjoy what I do. That is why I am a teacher. Because I like to teach.

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