Elasticity – Percentage change in one variable resulting from a 1% increase in another.
Price Elasticity of Demand – Percentage change in quantity demanded of a good resulting from a 1% increase in its price.
E/p = P ΔQ/ Q ∆P =% ΔQ/ % ∆ P
Infinitely elastic demand – Principle that consumers will buy as much of a good as they can get at a single price, but for any higher price the quantity demanded drops to zero, while for any lower price the quantity demanded increases without limit.

Completely inelastic demand – Principle that consumers will buy a fixed quantity of a good regardless of its price.

**The steeper the slope of the cure, the less elastic demand is.
Income elasticity of demand – Percentage change in the quantity demanded resulting from a 1% increase in income.
E1 = I ∆Q / Q ∆ I
Cross-price elasticity of demand – Percentage change in the quantity demanded of one good resulting from a 1% increase in the price of another.
EQP= P∆Q / Q ∆ P
When goods are substitutes, cross-price elasticities will be positive. When goods are complements, cross-price elasticities will be negative.
Price elasticity of supply – Percentage change in quantity supplied resulting from a 1% increase in price.
Point elasticity of demand – Price elasticity at a particular point on the demand curve.
Arc elasticity of demand – Price elasticity calculated over a range of prices.
E = ( ∆Q ¿( P´ )
p ∆ P Q´