Let f(x) = 4x. (a) Sketch the region R under the graph of f on the interval [0,2]. 1 2 3 Find its exact area using geometry. square units (b) Use a Riemann sum with four subintervals of equal length (n = 4) to approximate the area of R. Choose the representative points to be the right endpoints of the subintervals. square units (c) Repeat part (b) with eight subintervals of equal length (n = 8). square units