2.1. a. Compute 4! 2 22 23 24 b. Write the alternating series 1 - 1 + 2 - 2 -1 3 -3 -2 -1 + 4 - 4 - 3 - 2- 1 using sigma notation and make it look like (-1) "by M-1 HELP: n! = n(n -1)(n - 2) - - - 3 . 2 - 1 C. Identify the positive part of the general term. d. Show that the sequence {be ] is decreasing using the definition of a decreasing sequence e. There is a theorem that says n! > 2". Use this and show that for the b,, in part (b) that the following double inequality holds 0