stockjaguar

Check out Book 2, page 173 Picture of Perfect competition;
I think I am correct in saying every firm, no matter the competition, sets quantity output at MR=MC.
In perfect competition MR = Demand curve = Price, so the MR=MC equilibrium also determines price. If this equilibrium point is below ATC then yes it is economic loss (as you will see on page 173).
Now flick over to page 193, you see what happens in Monopoly.
Output is determined by MC=MR, however, price is not.
Price is set as per the Demand curve (which is of course downward sloping unlike for the perfect competition firm). Even if ATC is greater than the MC=MR point, so long as it remains below Demand curve its profit.
Hope I haven’t said anything wrong here