# Spreadsheet for calculating slopes at points on quadratic functions

On the Physics Modeling email list there has been a discussion of finding tangents to a parabolic curve using an Excel spreadsheet. The primary way we use this is when students graph position vs time of a ball rolling down a ramp. Students discover that the relationship can be modeled as a parabolic equation, x = at^{2}+bt+c. If they can calculate the slope (velocity) at various times, they can then graph velocity vs time, and discover that this relationship is linear.

I have created a spreadsheet that will allow students to enter the their (1) quadratic function values, (2) Independent Variable range, (3) a chosen Independent Variable value and (4) the increment above and below it. The spreadsheet will then calculate and graph the “tangent” at that point (not exactly the tangent, but if they chose a small enough increment, it will look like a tangent).

A screenshot of the spreadsheet is below, and you can download a copy of the spreadsheet here.