And as you see right over here, if you look at it, the f of 1 is just going to be 0, so you're going to have f of 2 times, so it's going to be this height times this base times 1 half, which is just the area of a triangle. But let's look at the second trapezoid, trapezoid 2. Right over here. What is its area going to be? Well, it's going to be f of 2 plus f of 3. f of 2 is this height, f of 3 is this height, so we're taking the average of those two heights, divided by 2, that's the average of those two heights, times the base, times delta x. And then let's do trapezoid 3. I think you're getting the idea here.