Each part defines a non-empty set A and a function f on A. First determine whether A is a convex set; if so, determine whether f is concave, convex or neither. (You do not need to determine whether f is strictly concave or strictly convex.) 1. A = f{(x; y; z) R3 : x is an odd number} and f(x; y; z) = x^2 + y^4 + exp(z) for all (x; y; z) A. (An odd number is an integer that is not divisible by two.) 2. A = f{(x; y; z)R3 : x + y + z > 0} and f(x; y; z) = (x^2 + y^2 + z^2)^1/2 for (x; y; z) A. 3. A = f{(x; y)R2 : 0 < x < 3; and y > 0} and f(x; y) = yx(3x) for (x; y) A. 4. A = f{(x; y; z) R3: x^4+y^4+z^4 > 0} and f(x; y; z) = log(x^4+y^4+z^4) for (x; y; z) A.