(i) S22 - S19 = 22*23 - 19*22 = 4*22 = 88
(ii) S1 = 1*3 = 3 = 1st term
S2 = 2*4 = 8 = 1st + 2nd = 3 + 2nd so the 2nd term is 5
S3 = 3*5 = 15 so the 3rd term is 7
The sum Sn of the first n terms of a sequence is given by Sn=n(n+2).
Find:
(¡) the sum of the twentieth,twenty-first and twenty-second terms of the sequence;
(¡¡) the first three terms of the sequence.
1 answer