Kevin’s utility function is U(x, y) = x a + y b , where a ≥ 0 and b ≥ 0. What additional restrictions on the values of the parameters a and b are imposed by each of the following assumptions? (note: some of the following notions we mentioned in passing during lectures, e.g. homotheticity, normal goods, but the textbook provides the necessary additional information) (a) Kevin’s preferences are homothetic. (b) Kevin’s preferences are homothetic and convex. (c) Goods x and y are perfect substitutes. (d) Kevin’s preferences are quasi-linear and convex, and x is a normal g