Question

If S_r denotes the sum of the first r terms of an A.P. Then , S_3n: (S_2n − S_n) is

(a) n

(b) 3n

(c) 3

(d) none of these

Answer 1

Here, we are given an A.P. whose sum of r terms is S_r. We need to find.

Here we use the following formula for the sum of n terms of an A.P.,

Where; a = first term for the given A.P.

d = common difference of the given A.P.

n = number of terms

So, first we find S_3n,

Similarly,

Also,

So, using (1), (2) and (3), we get,

Taking common, we get,

Therefore,

Hence, the correct option is (c).