The law of demand is a fundamental concept in economics that states that as the price of a product or service increases, the quantity demanded of that product or service decreases, all other things being equal. This relationship can be mathematically expressed as:
Qd = f(P)
where Qd represents the quantity demanded, P represents the price of the product or service, and f() represents the functional relationship between them. In simpler terms, this means that the quantity of a product or service that people are willing and able to buy will decrease as its price increases.