Multiple choice

What is the 10th term of the sequence -9, -6, -1, 6, 15,...?

  1. 60

  2. 70

  3. 80

  4. 90
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D Correct answer
Explanation

The sequence is -9, -6, -1, 6, 15. The differences between consecutive terms are 3, 5, 7, 9. This is an arithmetic progression of differences starting from 3 with a common difference of 2. The nth term is -9 + sum of the first (n-1) terms of the difference sequence, which is -9 + (n-1)(3 + (n-2)). For n=10, term = -9 + 9(3 + 8) = -9 + 99 = 90.

AI explanation

The sequence follows a pattern of perfect squares subtracted by 10, specifically n^2 - 10. For the 10th term, substituting n = 10 gives 10^2 - 10 = 90. The result is 90.

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