The regression models that we introduced in Sections 14.2 and 14.6 are linear in the x€™s, but, more important, they are also linear in the ’s. Indeed, they can be used in some problems where the relationship between the x€™s and y is not linear. For instance, when the regression is parabolic and of the form

We simply use the regression equation µY|x = β0 + β1x1 + β2x2 with x1 = x and x2 = x2. Use this method to fit a parabola to the following data on the drying time of a varnish and the amount of a certain chemical that has been added:

Also, predict the drying time when 6.5 grams of the chemical is added.

Amount of additive grams) Drying time (hours) 8.5 8.0 6.0 5.0 6.0 5.5 6.5 7.0