Elasticity, as a mathematical concept, refers to the relative change rate, that is, the percentage 1% of the change of the dependent variable caused by the change of the independent variable, so elasticity is a measurement method that does not depend on any unit, that is, dimensionless.

In real life, such problems often occur. The price of commodity A rose from 10 yuan/piece to1yuan/piece, and the price of commodity B rose from 1000 yuan/piece to100/yuan/piece. The absolute changes in the prices of the two commodities are the same, but their substantive meanings are different. Obviously, the increase of commodity A is much greater than that of commodity B. Therefore, in economic activities, we should not only analyze the absolute changes of some economic quantities, but also consider the relative changes of some economic quantities. If there is a certain functional relationship between two economic quantities, it is necessary to consider the degree of influence of the change of one economic quantity on the other, and this degree of influence is elasticity.

The concept of elasticity in economics comes from the meaning of change rate in mathematics. That is to say, it should be understood as the change of dependent variable 1 unit, and the degree of change of independent variable is the elasticity of dependent variable to independent variable. That is to say, it includes two aspects: first, A and B must have a causal relationship. For example, because the number of buyers decreases due to the price increase, there is a causal relationship between the price and the purchase quantity, which satisfies the first condition of forming an elastic relationship; Second, the relationship of elasticity should be expressed by the following formula: elasticity =(△y/y)/(△x/x). Take the relationship between price and purchase quantity: elasticity = [(purchase quantity after price increase-purchase quantity before price increase)/[(new price-original price)/original price].