And their height seems to be based on, their height seems to be based on the midpoint. So between the start, between the left side and the right side of the rectangle, you take the value of the function at at the middle value right over here. So for example, this height right over here looks like f of one. This height right over here looks like f of three. This height of this rectangle is f of five. This height right over here is f of seven. So given the way that this has been constructed, and we want to take the sum of the areas of these rectangles as an approximation under, as the area under this curve, how would we write that as sigma notation?