So let's do trapezoid, or I really should say triangle, this first shape, whatever you want to call it. What is the area of that going to be? Well, the area of a trapezoid, and you'll see this will just turn into the area of a triangle, it's the average of the heights of the two sides of the trapezoid, the way we've looked at it, or you could say the average of the heights of the two parallel sides, I guess is the best way to say it. So f of 1, that's the height here, plus f of 2, all of that over 2, and then we're going to multiply it times our delta x. Actually, let me do that in that same red color to show you that this is the area of that first trapezoid. So times delta x. 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.