C=q2
MC=2q
P=12−q
TR=p×q
=(12−q)×q
=12q−q2
MR=12−2q
a) For profit Maximization,
MR=MC
12−2q= 2q
4q=12
q=3
P=12−3=9
Π= TR-TC
TR=9×3=27
TC=32=9
∴ Π =27-9=18
b) Diagram

c) If a tax of $2 is imposed.
Because the tax increases the price of each unit, total revenue for the monopolist decreases by TQ, and marginal revenue, the revenue on each additional unit, decreases by T;
MR=12−2q−T
∴MR=10−2q
New profit Maximization
MR=MC
10−2q=2q
4q=10
q=2.5
P=12−q−T
=12−2.5−2=7.5
TC=q2
=2.52=6.25
TR=p×q
=2.5×7.5=18.75
∴Π=18.75−6.25
=12.5
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