Previous Problem Problem List Next Problem (1 point) a) The rectangles in the graph below illustrate a| left endpoint + Riemann sum for f(x) = 4 sin x on the interval [0, it]. The value of this Riemann sum is 13 A N 1 -pi/2 pi/2 PI 3pi/2 -1 -3 -4 -5 Left endpoint Riemann sum for y = 4 sin x on [0, x]