How is a good classified when it has a negative cross elasticity of demand?

A good is classified as a complement when it has a negative cross elasticity of demand. This indicates that as the price of one good rises, the quantity demanded for the other good falls. This relationship often occurs with goods that are used together, due to the fact that an increase in the price of one good may lead consumers to buy less of it and, consequently, also buy less of its complementary good.

For instance, consider the relationship between printers and ink cartridges. If the price of printers increases, the demand for ink cartridges might decrease because consumers are less likely to purchase printers, which means they will also need fewer ink cartridges. Thus, the negative cross elasticity signifies that the two goods are complements, enhancing the understanding of how these goods interact in the market.