Quadratic Regression illustration

The GeoGebra worksheet below illustrates quadratic regression for six data points. Initially, the data points all lie on a single line, and the quadratic goes right through them as a line. However, when you click and drag the points, the regression function will change but will always be the "best fit" to the data points.

Here are the commands needed to make this illustration. Enter them one by one in the Input box.
P=(1,1)
Q=(2,2)
R=(3,3)
S=(4,4)
T=(5,5)
U=(6,6)
A = {P, Q, R, S, T, U}
f = FitPoly[A,2]
Options, Rounding, 5 decimal places

Craig L. Zirbel, Created with GeoGebra