The common difference of an A.P., the sum of whose n terms is Sn, is

Answer: Option A

Sum of n terms = S_n
∴ a_n = S_n - S_{n - 1}
and a_{n - 1} = S_{n - 1} - S_{n - 2}
∴ Common difference (d) = a_n - a_{n - 1}
= (S_n - S_{n - 1}) - (S_{n - 1} - S_{n - 2})
S_n - S_{n - 1} - S_{n - 1} + S_{n - 2}
= S_n - 2S_{n - 1} + S_{n - 2}