iintervals. In Exercises 13-16, find an approximation of the area of the region R under the graph of the function fon the interval [a, b]. In each case, use n subintervals and choose the representative points as indicated. 13. f(x) = x2 + 1; [0, 2]; n = 5; midpoints 15. f(x) = -; [1, 3]; n = 4; right endpoints