I want to find a linear approximation, approximation of f, of f around, and you need to know where you're going to be approximating it, around x equals negative one. So what do we mean by that? Well, let's look at this graph over here. On this curve, when x is equal to negative one, f of negative one is negative, is negative one half, which sticks us right over there. Let me do this in a better color. So it's right over there. And what we want to do is approximate it with a line around that.