Complementary products are the ones in which if the demand for one product rises when the cost of another product decreases, that means. For example, printers and cartridges, if the cost of printers is decreased, this would result in excessive demand for cartridges since the printers are available for a cheap cost. Thus increasing the demand for cartridges. This we can put it as complementary products are those having negative cross elasticity of demand.If the cost of one product increases, the cost of other product also increases.
Conversely, in substitute products, if the cost for one product is decreased, the cost of another product also decreases.If the cost of one product increases, the cost of other product also decreases..