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96. The constant term is not always needed in the regression equation. For example. many physical principles involve proportions. where no con- stant term is needed. In general. if the dependent variable should be 0 when the independent vari- ables are 0, then the constant term is not needed. Then it is preferable to omit :80 and use the model Y=lxl+BZXZ+"'+,kak'f3. Here we focus on the special case k = l. a. Differentiate the appropriate sum of squares to derive the one normal equation for estimat- ing .31- b. Express your normal equation in matrix terms, X'X = X'y, Where X consists of one column with the values of the predictor vari- able. c. Apply part (b) to the data ofExample 12.32. using hp fory and just engine size in X