If the sum of first n terms of an A.P. is cn2, then sum of squares of these n terms is?
If a is 1st term and d is common difference, sum of n terms = (n/2) (2a + (n-1)d) = (2an-nd) + n2d
comparing this with cn2 we get : 2an-nd = 0 and d = c => a = c/2, d = c
sum of squares of n terms =