Figure 2.17 Perfectly Inelastic and Perfectly Elastic Demand or Supply Curves
(a) When a demand or supply curve is vertical, its slope is infinite and it is perfectly inelastic. In other words, any change in price will result in a 0% change in quantity demanded or supplied.(b) When a demand or supply curve is horizontal, its slope is zero and it is perfectly elastic. In other words, any change in price will result in an infinitely large change in quantity demanded or supplied.