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Let f(x ) = 4x. ( a ) Sketch the region R under the graph of f on the interval [0, 2]. 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 left endpoints of the subintervals. square units (c) Repeat part (b) with eight subintervals of equal length (n = 8). square units (d) Compare the approximations obtained in parts (b) and (c) with the exact area found in part (a). Do the approximations improve with larger n? O Yes NO