5.5 As defined in Chapter 3, an indifference map is homothetic if any straight line through the origin cuts all indifference curves at points of equal slope: The MRS depends on the ratio Y/X.

a. Prove that in this case X/I is constant.

b. Prove that if an individual’s tastes can be represented by a homothetic indifference map, price and quantity must move in opposite directions; that is, prove that Giffen’s paradox cannot occur.