JEE Advanced · 2007 · 08 Apr 2007 · Paper 1 · Sequences and Series

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Let denote the sum of the first terms of an arithmetic progression (A.P.) whose first term is and the common difference is . Let


is always
  1. (A)an odd number
  2. (B)an even number
  3. (C)a prime number
  4. (D)a composite number✓ Correct

Answer: (D)

Solution

From the previous calculation:



Therefore,

Factoring:

Since is a product of two factors both greater than 1 for , it is always a composite number.

JEE Advanced · 2007 · 08 Apr 2007 · Paper 1 · Single correct option

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