Let f(x) = 9+ 4x. (a) Estimate the area under the graph of f, the x-axis, and the lines x = -1 and x = 2 using three rectangles and a right endpoints. R- Improve your estimate by using six rectangles. R6= Sketch the curve and the approximating rectangles for R3. y 25 35 25 20 0-1 15 10 20 20 15 15 10 5 y 25 20 20 2001 15 15 101 5