Mr. Gardner’s Mathematics Class
name _______________________________
Using Quadratic Regression to find a Curve of Best Fit with GeoGebra.
When you open the GeoGebra applet here is what you will see:
Pan and
Zoom
Tools
Algebra
Window
Grid
Spreadsheet
Enter
Points Here
Input
Bar
Instructions
Step 1: Entering Points
In the spreadsheet on the right, type in your table of values so that the x coordinates (the
independent variable) is in column A, and the y coordinates (the dependent variables) are in
column B.
Step 2: Plotting the Points on the Grid
Click and drag on all of the cell you have entered in the spreadsheet so that they are all
“highlighted.” Right click on the mouse (or on an apple computer hold down the control key and
click the mouse). Select the option “Create List of Points” and let go. You should see the list of
points on the axis, and in the algebra window on the left, you should see “list 1 = {(all of your
points will be listed here}}.
Step 3: Adjusting the Grid to your Data
Now you should adjust your grid to match your data. Look at the range and domain of your data.
With the mouse, right click on the grid and select “Graphics View”, and a window should come up
with tabs. You can alter the fields in your tabs for the x-axis, and y-axis to match your domain
Mr. Gardner’s Mathematics Class
name _______________________________
and range so that the grid displays the data points clearly. There are many other features you can
change in the Graphics View menu, so it may be worth your while to explore and experiment.
There is also a “pan” tool, and two zoom tools (in and out) on the tool bar.
Step 4: Regression, or Determining a Quadratic of Best Fit
To find your quadratic function of best fit, enter the following in the Input bar underneath the
graph,
FitPoly[list1,2]
and press enter. You should see the quadratic function of best fit on your screen, and you should
see the equation of the quadratic of best fit in the algebra window. If you right click on the curve
and select “Object Properties” you can change many features of the curve, such as its thickness
and its colour. You can also have it show both its name and value, which means that it will display
the equation of the quadratic of best fit beside the curve.
A note on the syntax you typed into the input bar.
You are doing a polynomial curve fit.
The list of points should be list 1 as displayed in the algebra window on the left.
You want degree 2, because degree 2 is a quadratic function.
So: FitPoly[list of points, Degree n of polynomial]
You can now answer all of the questions asked regarding your curve of best fit, then print and/or
save your graph prior to doing the next question.
To make a new graph for the next question, either close and re-start the applet by using the
button, or simply delete all entries in the spreadsheet and start the next question.