division by zero is a concept, it cannot be numerically expressed.
For example, let's talk chemistry, a reaction occurs in equilibrium (i'm not bothered thinking of chemicals). At equilibrium, there are 0 moles of reactant and 1 moles of each product. This would mean that Kc would be the following equation ((1)(1))/((0)(0)). which goes down to 1/0. Some people would say that this is impossible and leave it in the dirt. However, since we know the context of this sum, we can say that Kc approaches infinity, because all the reactants will eventually react. This can be said for the other way, but i'm not going to say anymore on that than this.