Do some "reverse engineering" to determine the type of approximation (left sum, midpoint sum, etc.) and identify f (x), a, b, n, Ex, and x k. Then sketch the approximation described. 100 19. sin(0.05(k 1)) + sin(0.05k) (0.05) k=1 (1+) + (1+ $) (1) 9 20. k=1 113 2.