A sequence begins and its second differences are constant. What is the th term?

Answer and explanation

Correct answer: D.

  1. Step 1: First differences: . Second differences: , so the coefficient is .
  2. Step 2: Subtract from the terms: , , , so the remainder is the constant .
  3. Step 3: The th term is .
Answer
.
Why not the others: : gives for but for . : gives for but for . : gives for but for .

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