1.Define elasticity. What are the price elasticity of demand, price elasticity of supply, income elasticity of demand and cross elasticity of demand?

2.There are two types of products such as complementary goods and substitute goods for your own products. How you can use the cross elasticity of demand to determine whether some products are complementary goods or substitute goods of your own goods? For example, if the cross elasticity of demand is negative, is a product of your competitors complementary goods or substitute goods? If the income elasticity of demand of your goods is negative, is your goods inferior goods or normal goods?