i)than the condition of profit maximization
ii)Marginal costs (MS) are constant. In each market, the monopolist firm, maximizing profit when MR = MS is equal, sets a higher price (RD at which the demand for its goods is less elastic.
The word "discrimination" has a negative connotation: it is perceived as a violation of rights. But in the third degree of price discrimination, buyers often participate consciously and voluntarily, for example, buying premium products (premium alcohol or niche perfume), paying for any VIP class services, a ticket to the premiere of a play, a new collection of clothing, new digital technology (another new iPhone model, which in six months will cost much cheaper). First, at a high price, the product is purchased by those for whom image and prestige are important. When the price goes down, it's the turn of people with less purchasing power. At the same time, the quality and configuration of the product remains the same. Thus, third-degree price discrimination helps to cover the market more widely.
Third-degree price discrimination leads to a partial capture of the consumer surplus by the seller.