Find the nth term of the quadratic sequence 2, 9, 20, 35, ...
Answer and explanation
Correct answer: A.
- Step 1: First differences: 7, 11, 15. Second differences: 4, 4, so the nth term starts .
- Step 2: Subtract (2, 8, 18, 32) from the sequence: 0, 1, 2, 3, which is .
- 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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