Question

Find r^th term of an A.P. whose sum of first n terms is 2n+3n^2.​

Answer 1

Answer:

Given that sum of n terms of an AP.

Sn = 2n + 3n²

Tn = Sn-Sn-1

= (2n + 3n²) − [2(n − 1) + 3(n − 1)²]

= (2n + 3n²) — [2n − 2 + 3(n² + 1 − 2n)]

= (2n + 3n²) - (2n − 2 + 3n² + 3 − 6n)

= 2n + 3n²2n + 2- 3n²-3+ 6n

= 6n - 1

rthterm Tr = 6r- 1