235: 22/HP.. S CASPA | Applicant... CASPA Course Su.. Do's and Don'ts f.. 4.2 Riemann Sums OPEN am The rectangles in the graph below illustrate a left endpoint Riemann sum for f(2) = + 2x on the interval [4, 8]. The value of this left endpoint Riemann sum is , and this Riemann sum is equal to O the area of the region enclosed by y = f(x), the x-axis, and the vertical lines x = 4 and x = 8. Left endpoint Riemann sum for y = = + 2x on [4, 8]