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Economics Problem 10.3 (concavity) Using the Hessian characterization of concave and convex functions: i) Find whether the following functions are concave, convex, both or either? ii) Do they have stationary points, global maxima, or minima? iii) Find optimal values for global maxima and minima if any. a ) y = x, + x2 b)y = -x7 - x2 c)y = (x1+ x2) 2 d) y = - Ex? c) y = x1 + 3x1X2 + 6x, + x3 ~ f) y= -x3 - x3 - 2x1x2