Consider the following three supply curves: P = 2.25Q; P = 2+2Q; P = 6+1.5Q.
(a) Draw each of these supply curves to scale, and check that, at P = $18, the quantity supplied in each case is the same.
(b) Calculate the (point) supply elasticity for each curve at this price.
(c) Now calculate the same elasticities at P = $12.
(d) One elasticity value should be unchanged. Which one?