2. (i) Determine if the following function is concave or convex: u(x, y) = x¹/4y3/4, x≥ 0, y ≥ 0. [This type of a utility function, where the exponents add up to 1, is commonly referred to as the Cobb-Douglas utility function.] (ii) Decide for which values of the constant a the following function is concave, convex or neither: f(x, y) = -2x²-8y²+axy + 10ay.