An arithmetic progression has first term and common difference . If the sum of the first terms is , find .

Answer and explanation

Correct answer: B.

  1. Step 1: Apply the arithmetic series sum formula . Substituting and gives .
  2. Step 2: Clear the denominator to form a quadratic equation: . Factoring gives . Because must be a positive integer, .
Answer
.
Why not the others: Choosing gives ; choosing yields ; choosing gives .

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An arithmetic progression has first… | Singapore GCE A-Level