What will be an ideal response?
A perfectly elastic demand curve is horizontal and a perfectly inelastic demand curve is vertical. If the demand curve is vertical, then quantity demanded does not change when price changes, or the elasticity equals 0. Quantity demanded is completely unresponsive to changes in price. If the demand curve is horizontal, a tiny increase in price causes quantity demanded to go to zero. As the percentage change in price approaches zero, elasticity of demand approaches infinity. Quantity demanded is extremely responsive to even very small changes in price.