6. Use an approximation scheme using n -3 rectangles to estimate the area under the graph of f(x) -9-x2 and the interval [1, 3]. The height of the kth rectangle will be the value of f(x"), where x is midpoint of the kth interval. Fill in the missing entries in the table, and find the total area. Rectangle Left Right Midpoint, Rectangle Height Rectangle Endpoint endpoint Width x) Area 0.5 1.5 Total Area f(x) = 9-2 7. Let f(x)2x +1. (a) Use a simple area formula from geometry to find the area function A(x) that gives the area between the graph of f and the interval [0, x.J.(See last page for some formulas.) (b) Find A' (x), and confirm that A'(x) = f(x).