F(x) = 9 − x2 from x = 1 to x = 3; 4 subintervals (a) approximate the area under the curve over the specified interval by using the indicated number of subintervals (or rectangles) and evaluating the function at the right-hand endpoints of the subintervals. (see example 1.) (b) approximate the area under the curve by evaluating the function at the left-hand endpoints of the subintervals.