Cost functions in monopoly:

In the theory of monopoly, the shape of the cost curves are the same as in the theory of perfect competition. The average variable cost (AVC), marginal cost (MC) and average total cost (ATC) curves are 'U' shaped, while the average fixed cost (AFC) curve is a rectangular hyperbola. However, in monopoly the particular shape of the cost curves do not make any difference to the determination of the equilibrium, provided that the slope of the MC curve is greater than that of the MR curve. Monopoly differs from the perfect competition in respect of the interpretation of the marginal cost curve. Unlike perfect competition, in monopoly the MC curve is not the supply curve of the producer.

In fact, in monopoly there is no unique relationship between price and quantity supplied.