In the last exercise you saw that the linear model had some deficiencies. Let s create a better model.
a) Perhaps the cross-sectional area of a tree would be a better predictor of its age. Since area is measured in square units, try re-expressing the data by squaring the diameters. Does the scatterplot look better?
b) Create a model that predicts Age from the square of the Diameter.
c) Check the residuals plot for this new model. Is this model more appropriate? Why?
d) Estimate the age of a tree 18 inches in diameter.