Instructional Unit 4

Fitting Functions to Parabolic Data

by Sandy Cederbaum

Our goal in Unit 4 will be to try to find a rule for a given parabola or given data that is parabolic in nature. We will write this rule in vertex form which we studied in Unit 2 and Unit 3. This form of a quadratic equation is called vertex form because the coordinate (h,k) is the vertex of the parabola.

You will need a TI-83 graphing utility and you may need to do a little guess and check in order to find the best fitting rule. We will go through one example of how we might attack this problem and then we will load a program on the TI-83 graphing calculator that will enable you to practice this skill.

Example: Find the rule for the function that best fits the following graph:

If you had any trouble with this example, here is some strategy you can try.

Now we are ready to load a program onto your graphing calculator. The program is called PARAB. I will have a copy in class that you may download using the graphing link. This program can also be found on the Texas Instruments website. The following link gives you information about how to download programs from this site. At the top of the page is a link to the program archives. This is a useful website that you might want to bookmark and explore on your computer.