Let f(x) = 3x + 4, x1 = 2, X2 = 3, X3 = 4, X4 = 5, and Ax = 1. 4 (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) _ f ( x; ) Ax = i = 1 (Simplify your answer.) (b) Find the definite integral that is approximated by the sum in part a. 4 _f ( x; ) Ax~ ] dx i = 1