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

S_2n = \(\frac{2n}{2}\)(2a + (2n–1) d) 

S_n = \(\frac{n}{2}\)(2a + (n–1)d) 

S_3n = \(\frac{3n}{2}\)(2a + (n–1)d)