We saw that in the last example. So that's what we want to do. And we saw in the last, I think it was two videos ago, that we defined f prime of x to be equal to just the, well, I'll write it this way. It's the slope of the secant line between x and some point that's a little bit further away from x. So the slope of the secant line is change in y. So it's the y value of the point that's a little bit further away from x. So f of x plus h minus the y value at x, right?