But where you want to approximate it with a linear function, especially around a certain value. And so what we're going to do is we want to find an approximation. Let me write this down. I want to find an approximation for, and actually let me be clear. I want to find a linear approximation. So I'm going to approximate it with a line. 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.