(i) State the general term formula and the formula for the sum of the first n terms of an arithmetic progression.
(ii) Show algebraically how the common difference can be eliminated from these two formulas to obtain a single relation connecting a (first term), Sn (sum of first n terms) and an (the n-th term).
(iii) For the arithmetic progression 3,7,11,…, take n=5 and verify the relation obtained in part (ii).