Fill in the blanks. a. In the polynomial regression equation y = 5 + 3x− 2x2 + 7x3 + 9x4, the cubic effect coefficient is ________. b. In polynomial regression, we usually ________.a predictor...

Fill in the blanks.

a. In the polynomial regression equation y = 5 + 3x− 2x2 + 7x3 + 9x4, the cubic effect coefficient is ________.

b. In polynomial regression, we usually ________.a predictor variable to reduce the correlations between its powers.

c. In the forward selection method of polynomial regression, we add increasing powers of the predictor variable until the t-test for the utility of the highest-degree term is ________.

d. The second-order polynomial regression equation relating a response variable y to two predictor variables x1 and x2 is given by _______.