Find the nth term of the quadratic sequence 2, 9, 20, 35, ...

Answer and explanation

Correct answer: A.

  1. Step 1: First differences: 7, 11, 15. Second differences: 4, 4, so the nth term starts .
  2. Step 2: Subtract (2, 8, 18, 32) from the sequence: 0, 1, 2, 3, which is .
  3. Step 3: So the nth term is .
Answer
.
Why not the others: gives 4, 11, 22, gives 2, 14, 34 and gives 2, 10, 24.

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