13. (8 points) Consider the following Riemann sum: n 2 lim n- oo n i=1 a. Find the limit of the Riemann sum directly. b. To which integral does the Riemann sum correspond? 14. (4 points) Approximate the area under f (x) = 16 - x* on the interval [-1,1] with four rectangles using right endpoints. 15. (4 points) Use Property 8 from Section 4.2 to estimate the following integral. (16 - x4) dx -1