Complementary good
In microeconomics, complementary goods are goods whose utility is increased if they are consumed together. This means that the demand curve for both goods will move in the same direction, if the price changes. If the demand curve does not change in the same direction, in case of a price change, the goods are substitute goods.
Complementary Good Media
Complementary goods exhibit a negative cross elasticity of demand: as the price of goods Y rises, the demand for good X falls.
Supply and demand of cars when the price of petrol decreases
Indifference curve for perfect complements
