Let f(x) = 2x + 3, X1 = 0, X2 = 2, X3 = 4, X4 = 6, and Ax = 2. (a) Find _f (x;) Ax. i = 1 (b) The sum in part (a) approximates a definite integral using rectangles. The height of each rectangle is given by the value of the function at the left endpoint. Write the definite integral that the sum approximates. . . . 4 (a) E f ( x; ) Ax = i = 1 (Simplify your answer.)