(a) Define an arithmetic progression.
(b) Consider the sequence 2, 5, 9, 13.
(i) Find the differences between successive terms.
(ii) State, with reason, whether or not the sequence is an arithmetic progression.
(c) If your conclusion in part (b) is that the sequence is an arithmetic progression, write its common difference. If it is not an arithmetic progression, identify the pair of consecutive terms that break the required condition.