Refer to the data of Exercise 13.41. Suppose that another variable was controlled, that the first four squares at each speed were treated with a .2 concentration of protective coating, and that the second four squares were treated with a .4 concentration of the same coating. Given that x1 de-notes the machine speed and x2 denotes the concentration of the protective coating, fit these models:
y = β0 + β1x1 + β2x12 + β3x2 + ɛ
y = β0 + β1x1 + β2x21 + β3x2 + β4x1x2 + β3x21x2 + ɛ
In exercise

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Machine Speed (rev/min) Wear 100 120 140 160 180 200 23.0, 235,24.4,25.2,25.6, 26.1,24.8, 25.6 26.7,26.1,25.8,26.3,27.2, 279,283,274 28.0,28.4.27.0,28.8,29.8, 294, 28.7,29.3 32.7, 32.1,319, 33.0.33.5, 33.7, 34.0, 325 43.1, 41.7.424, 421, 43.5, 43.8, 44.2.436 54.2, 43.7,53.1, 53.8.55.6, 55.9, 54.7,54.5