Given function f(x)=x^3 - 2*x + 4. Let [-1.5, 1.5] state the interval. a. Partition interval into 6 sub-intervals. Let u1,u2,...,u6 be centers of sub-intervals. Calculate f(u1),...,f(u6), and use the values to find area under curve. b. Partition interval into 12 sub-intervals. Repeat process, as in part a. c. Graph function (but not all rectangles). Compare results of parts a and b.