Let an be the nth term of an A.P. If ∑r=1100 a2r=α and ∑r=1100 a2r−1=β, then the common difference of the A.P. is:
α-β
1100α-β
β-α
1200α-β
Let d the common difference of the A.P., then α−β=∑r=1100 a2r−a2r−1=∑r=1100 d=100d⇒ d=1100(α−β)