If Sn, denote the sum of n terms of an A.P. with first term a and common difference d such that , is independent of x, then
Given AP in which First term = a, Common difference = d, Number of terms = n
And Sn denotes the sum of n terms
So
and
Now,
If d= 2a
Sx /Skx = (2×a) / (k2×2a)
= 1/ k2
So Sx /Skx is independent of if d = 2a