Answer: The demand is shared with the new company that enters the market.
Explanation: The Cournot duopoly is an imperfect competition model, that is, the law of supply and demand is not freely used, in which two companies with equal costs compete with homogeneous goods in a static environment, that is, with the same characteristics.
For example: A leading brand of soda in the market, get a competitor that has the same characteristics. People will prefer one of the two brands and they will always lead the market, but they will have to divide the market.