The profit maximization principle for both a perfectly competitive firm and a monopoly is MR=MC. However, a monopolist usually does not use the MR = MC principle to determine price. Explain with appropriate examples. Bonus points for graphical analysis.

Graphically explain the concept of kinked demand curve and how this model is used by oligopolists to determine price and output.

Provide an example of a monopolistically competitive firm and an oligopoly firm. With appropriate graphs, show at least two features which distinguish the price and output determination of these firms.