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.

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

Craig L. Zirbel, Created with GeoGebra