So this region right over here is the base of a three-dimensional figure. And what we know about this three-dimensional figure is if we were to take cross sections that are perpendicular to the x-axis, so cross sections, I guess we could say, that are parallel to the y-axis. So let's say we were to take a cross section like that. We know that this will be a semicircle. So if we take a slightly different view of the same three-dimensional figure, we would see something like this. I've kind of laid the coordinate plane down flat and I'm looking at it from above. So this cross section, if we're looking at it at an angle, and if the figure were transparent, it would be this cross section right over here.