The aim of monopolist is to maximise profit therefore; he would produce that level of output and charge that price which gives him maximum profits. He would be in equilibrium at that output and price at which his profits are the maximum. Or we can say that he will be in equilibrium position at that level of output at which marginal revenue equals marginal cost. In order to attain equilibrium, monopolist must satisfy 2 conditions:

Marginal cost must be equal to marginal revenue.

The marginal cost curve must cut marginal revenue curve