We saw that when we constructed it. This is going to be the g of x at that value. So even though the rectangles look like they're kind of shifted around a little bit, and they're actually all shifted up by the f of x, the heights of these rectangles that I'm drawing right over here are exactly the same thing as the heights of the rectangles that I'm drawing over here. They, once again, they are all just shifted up and down by this f of x function, but these are the exact same rectangles, or they have the exact same heights. And the limit as you get more and more of these by making them thinner and thinner is going to be the same as the limit as you get more and more of these as you get thinner and thinner. And so this area right over here, and I'm obviously not doing a rigorous proof, I'm giving you the intuition for it, is the exact same thing as this area right over here. So the area under this curve, the definite integral from a to b of f of x plus g of x dx, is just going to be the sum of these two, is just going to be the sum of these two definite integrals.