Question

find common difference of AP if sn=2n2+n

Answer 1

Tn = Sn - Sn-₁

Tn = 2n² + n - 2(n-1)² - n - 1

Tn = 4n - 1

T1 = 4 - 1 =3

T2 = 8 - 1 = 7

So c.d. = 4

(Note -- If the Sn of AP is of the type an² + bn

common diffrence = 2a)