In the long run,these profits attract new firms with competing brands.The firm's market share falls,and its demand curve shifts downward. In long-run equilibrium,described in part (b),price equals average cost,so the firm earns zero profit,even though it has monopoly power. In the long run, these profits attract new firms with competing brands. The firm's market share falls, and its demand curve shifts downward. In long-run equilibrium, described in part (b), price equals average cost, so the firm earns zero profit, even though it has monopoly power