In a previous question we used rectangles on a grid to approximate the integral
where D is the ellipse with axes 6/5 and 1. This is equivalent to the double iterated integral
According to the theory of Riemann sums, this integral should equal the limit of the area of our approximation as the grid gets finer and finer.
How confident are you in your answer? (You may want to compute approximations for more grid sizes.)