QA=3QB
QA / (QA + QB) = 75% , QA = 3QB
πB=(100-2QB-QA)QB-(30QB+120)
=70QB-5QB2-120
dπB/dQB=0 ,70-10QB=0 ,
QB=7
QA = 21, PA = 200 - 42 - 7 = 151, πA = 151*21 - 50*21 - 350 = 1771
QB = 7 , PB= 100- 21 - 14 =65 , πB = 65*7 - 30*7 - 120 = 125
6樓是正解,因各有不同目標,無領導廠商,需聯立求解
Q=qa+qb
qa=75%Q=3/4Q===>qa=3qb