(1) A consumer has utility function U($1,.'B2) = VII/'1 + VII/'2. (a) In the same graph, draw the indifference curves {($1, $2) | U($1, $2) = 2} and identify the upper contour set {($1, $2) | U($1,$2) 2 2}. (b) Are his preferences monotone? (c) Are his preferences convex? Is U quasiconcave? Justify your answers formally. (2) Show that if the utility function U represents the preferences : on R1, then U is quasi- concave if and only if t is convex