The Total solution for NCERT class 6-12
If the sum of n terms of an A.P. is (pn + qn2),where p and q are constants, find the commondifference.
We know that,
Sn =n/2 [2a + (n-1)d]
From the question wehave,
On comparing thecoefficients of n2 on both sides, we get
d/2 = q
Hence, d =2q
Therefore, the commondifference of the A.P. is 2q.