n/2 (2a + (n-1)d) = 3n^2+2n
2an + dn^2 - dn = 6n^2+4n
dn^2 + (2a-d)n = 6n^2+4n
d = 6
2a-d = 4, so a = 5
Tp = 5+(p-1)(6) = 6p-1
check: the AP is
5,11,17,23,29,...
S1 = 5 = 3*1^2+2*1
S2 = 16 = 3*2^2+2*2
S3 = 33 = 3*3^2+2*3
S4 = 56 = 3*4^2+2*4
...
The sum of n terms of an a.p. Is 3n2+2n,then find its p'th term.
1 answer