The interesting thing is when you start working with limits. Lets say you have two equations that both equal zero at X=1, and lets say we divide one equation by the other. If we find the ratio at X=1, obviously that is undefined. But if we get reeeeallly close to X=1 (take the limit as X->1) the ratio can actually approach any number! Depending on the equation of course, I once devised an equation that was undefined at X=0, but the limit approached 42
