Question

The common difference of an A.P., the sum of whose n terms is Sn, is

A. Sn – 2Sn–1 + Sn–2

B. Sn – 2Sn–1– Sn–2

C. Sn – Sn–2

D. Sn – Sn–1

Answer 1

an is the nth term of an A.P and an–1 is the (n–1)th term of an A.P,

d = common difference,

Sn = sum of n terms of an A.P

d= an – an–1

But an= Sn – Sn–1

And an–1= Sn–1 – Sn–2

So d= Sn – Sn–1 – ( Sn–1 – Sn–2)

d= Sn – 2 Sn–1 + Sn–2