## Tuesday, July 1, 2014

### Some Things I Wish I Knew When I Started Using Geogebra

Using Geogebra as a demonstration tool for teaching concepts such as graphing and transformations can be amazing, but there is so much that can go wrong during the lesson.  After some pretty intensive play sessions with Geogebra and reading through a few tutorials such as this one by Gerrit Stols I was ready to try a demo in my class.

One of the first concepts I showed to students on Geogebra was how the factors of a polynomial function are related to its roots.  I typed in the function f(x)=x(x+2)(x-7) into the input bar at the bottom of the screen, hit enter, and below is what we see.

Not so great.  If I want my students to understand the nature of cubic functions, this is definitely not  what I want them to see.  Select "Move Graphics View" from the toolbar near the top of the screen, and then drag on either axis to rescale.  Drag in any quadrant to recenter.  When you are done, select the "Move" tool from the toolbar so you can select or move object.

The graph below looks better, but the students in the back still can't see the numbers on the axes.  The function will be hard to see on worksheets, so changing the line thickness can help as well.

To change the font size, select "Options" from the top of the page, then font size, then 24.

To change the line thickness right click on the function and select "object properties".  Select the "style" tab to change the line thickness.

The modified graph is much easier to see (and definitely appeals more to my inner interior designer).  There is also a tab for color under the object properties, which is especially nice if you want to build a graph matching activity.

One final must-have tip is to use a text box to display the equation for the function.  Select the "text" tool from the toolbar, click in the graphics view, type f(x)= and then from the objects menu select your function f.

Select the "move" tool and then drag the text box to a good location.

I made this document for a presentation to a math department that described themselves as low tech. Our focus for the day was transformations of functions, and so we focused on tools and settings that would apply to these presentations and images for worksheeets.  We walked through the steps on the document together, and I made screencasts for later use.  You can check out the screencasts below, though I'll give a fair warning that they were made at about 5am, pre-caffeine.