Approximate the integral integral integral integral f(x, y) da by dividing the rectangle r with vertices (0, 0), (4, 0), (4, 2), and (0, 2) into eight equal squares and finding the sum sigma 8 i = 1 f(xi, yi) where (xi, yi) is the center of the ith square. evaluate the iterated integral and compare it with the approximation. integral 4 0 integral 2 0 (x + y) dy dx sigma 8 i = 1 f(xi, yi) delta ai = integral 4 0 integral 2 0 (x + y) dy dx =