This is the key. If someone gives you any positive number epsilon for this function, as long as you make delta equal epsilon over 2, then any x within that range, that corresponding f of x is going to be within epsilon of our limit. This tells you, say the epsilon, and remember, it has to be true for any positive epsilon, but you could see how the game could go. If someone gives you the epsilon, let's say they want to be within 0.5 of our limit. Our limit is up here, so our epsilon is 0.5, so it would literally be the range I want to be between 10 plus epsilon would be 10.5, and then 10 minus epsilon would be 9.5. Well, we just came up with a formula. We just have to make delta equal to epsilon over 2, which is equal to 0.25, so that'll give us a range between 4.75 and 5.25.