If a perfectly competitive firm and a monopolistic competitor in long run equilibrium face exactly the same demand and cost curves, then there is high probability that the former will earn zero economic profits, but the latter will earn positive economic profits. both will earn zero economic profits, but the former will attain lower unit costs than the latter. both will earn zero economic profits, but the latter will attain lower unit costs than the former. both firms will earn zero economic profits, and attain the lowest possible unit costs. neither form will earn zero economic profits, but both will attain the lowest possible unit costs.
