But we want to square it, because that's going to give us the area of that cross section. And then, so let's do that. So times, I could say the absolute value of f of x minus g of x. I could just square that. Or if I want, I could just put parentheses there. I'll actually leave it as absolute value, since that's what I've already inputted into my calculator. And so that's going to give the area of each of those cross sections perpendicular to the x-axis. And you multiply it times dx.