This lecture explains the law, determining factors, the shape of the demand and supply curve, achieving equilibrium in quantity and price, achieving imbalance in quantity and price, the use of algebraic equations. Definition, determining factors, formulas, types and calculations of elasticity. Changes in demand due to prices and income, normal, inferior, substitute and complement goods. Substitution and income effects, consumer and producer surplus, individual and market demand, network externalities, demand estimation.