the monopoly firms aims at profit maximum under short run equilibrium with the case of zero cost profit maximization is reached at a point where TR is at maximum
Therefore..TR=TC
when TC is zero, profit is maximum..when TR is maximum
let us understand this with the following example
suppose there is a village which has only one well from which water is supplied to villagers. All villagers are completely depended on it. the well is owned by one person who purchase the water has to draw the water out of the well.the well owner is thus a monopolist with zero cost of production