For the sake of this video, we'll see in future videos that there's other ways of doing this, I'm going to use the left boundary of the rectangle to define the height, or the function, I should say. I'm going to use the function evaluated at the left boundary to define the height. So for example, for the first rectangle, this point right over here is f of 1. And so I will say that that is the height of our first rectangle. Then we go over here, the left boundary of the second rectangle. We're now looking at the function evaluated at 1.5, so that is f of 1.5. That's the height.