In an experiment to determine the minimum value on a certain four-dimensional re- spouse surface, with independent variables ,ng, s; E [-1, 1], a central composite design was employed and a second order model, parameterized as Elvx] = 3, + x'b + x'Bx. was fitted. The estimates (which are being reported in a simplified manner which makes for easy calculations), were 19 0 80= 1. b = 0 -1 (a) Estimate the stationary point of the surface. (b) Describe the nature of the stationary point - do you think it represents a mini- mum, or something else? (c) If the experimenter is willing to make further observations in order to better lo- cate the minimum, where would you advise him to look? Justify your