Q15 of 85 Page 110

If S1= 2 + 4 + ... + 2n and S2 = 1 + 3 + ... + (2n — 1), then S1: S2 = …..

We know that, Sn = × (a + l)


Where a = first term of the AP.


And l = last term of the AP


For S1,


We have S1 = × (2 + 2n)


⇒ S1 = n × (n + 1)


For S2,


We have S2 = × (1 + 2n – 1)


⇒ S2 = × (2n)


⇒ S2 = n2


Now = =


∴ =


∴ the correct option is (a)

More from this chapter

All 85 →
15

If 3 + 5 + 7 + 9 + ... upto n terms = 288, then n = ……

 15

Four numbers are in A.P. and their sum is 72 and the largest of them is twice the smallest. Then the numbers are ………

 15

For A.P., Sn — 2Sn – 1 + Sn – 2 =…. (n > 2)

 15

If Sm = n and Sn = m then Sm + n = ……