Producer Theory:
If asked to find a supply function for a firm in the long run, the easy for doing it is to compare AC to MC. In some cases though, that does not give the correct answer, and the profit function must be used. Can you advise in what cases this is true? When should I use a profit function, (and not the MC=AC shortcut), in order to find the supply curve of a 2 input firm in the long run?