So how would we do that? Well, one way to think about it, obviously there's many ways to express a line, but one way to think about it is, okay, it's going to, L of x is going to be, it's going to be, it's going to be f of four. It's going to be f of four, which is two. It's going to be f of four plus the slope, the slope at x equals four, which is of course the derivative, f prime of four. So that's going to be the slope of this line, of L of x is f prime of four. Let me make that clear. So this right over here is the slope, the slope when x is, at x equals four.