In: Economics
An industry contains two firms, one whose cost function is C(y) = 30y and another whose cost function is C(y) = y2. The inverse demand function for the firms' output is p = 120 -Q, where Q is the total output. What are the firms' outputs in a Nash equilibrium of Cournot's model? Graph the best response functions for Firm 1 and Firm 2.
The inverse demand is given to be 
 , and for 
 , we have 
 , where q1 and q2 are quantities of the respective firms.
Firm 1 have the cost function 
 , and its marginal cost would be 
 . The total revenue of firm 1 would be 
 , and the marginal revenue would be 
 . The profit maximization would occur where the MC is equal to MR,
ie 
 or 
 or 
 . This is the BR function of firm 1.
Firm 2 have the cost function 
 , and its marginal cost would be 
 . The total revenue of firm 2 would be 
 . and the marginal revenue would be 
 . The profit maximization would occur where the MC is equal to MR,
ie 
 or 
 or 
 .
The cournout (nash) equilibrium would occur where the BR
function intersects. Putting the first BR function into the second
one, we have 
 or 
 or 
 or 
 , and since 
 , we have 
 . These are the required equilibrium output.
The graph is as below.
