In Exercise- 12.28, we have the following data concerning wear of a bearing:

(a) The following model may be considered to describe this data:
yi = 00 + β1xl, + β2X2i + β12x1ix2i + ϵi,
for i = 1,2,...,6. The x1x2 is an "interaction"' term. Fit this model and estimate the parameters.
(b) Use the models (x), (x1, x2), (x2). (x1, x2, x1x2) and compute PRESS, Cp, and s" to determine the 'best'' model.

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