thumb|right|an example of a demand curve shifting. the shift from d1 to d2 means an increase in demand with consequences for the other variables  in economics, the demand curve is the graph depicting the relationship between the price of a certain commodity and the amount of it that consumers are willing and able to purchase at that given price. it is a graphic representation of a demand schedule. the demand curve for all consumers together follows from the demand curve of every individual consumer: the individual demands at each price are added together. demand curves are used to estimate behaviors in competitive markets, and are often combined with supply curves to estimate the equilibrium price (the price at which sellers together are willing to sell the same amount as buyers together are willing to buy, also known as market clearing price) and the equilibrium quantity (the amount of that good or service that will be produced and bought without surplus/excess supply or shortage/excess demand) of that market.krugman, paul, and wells, robin. microeconomics. worth publishers, new york. 2005. in a monopolistic market, the demand curve facing the monopolist is simply the market demand curve. ==characteristics== according to convention, the demand curve is drawn with price on the vertical (y) axis and quantity on the horizontal (x) axis. the function actually plotted is the inverse demand function. the demand curve usually slopes downwards from left to right; that is, it has a negative association (for two theoretical exceptions, see veblen good and giffen good). the negative slope is often referred to as the "law of demand", which means people will buy more of a service, product, or resource as its price falls. the demand curve is related to the marginal utility curve, since the price one is willing to pay depends on the utility. however, the demand directly depends on the income of an individual while the utility does not. thus it may change indirectly due to change in demand for other commodities. ==linear demand curve== the demand curve is often graphed as a straight line of the form q = a + bp where a and b are parameters. the constant âaâ embodies the effects of all factors other than price that affect demand. if income were to change, for example, the effect of the change would be represented by a change in the value of âaâ and be reflected graphic
Demand Economics_curves