Answer: (10 n+1 − 9n − 10)/9.
- A (10<sup>n+1</sup> − 9n − 10)/9
- B (10<sup>n+1</sup> − 10)/9 + n
- C (10<sup>n+1</sup> − 9n − 10)/81
- D 10<sup>n+1</sup>/9 − n
Correct answer: A. (10<sup>n+1</sup> − 9n − 10)/9
Explanation: Each term is 10<sup>k</sup> − 1, so the sum is (10<sup>n+1</sup> − 10)/9 − n = (10<sup>n+1</sup> − 9n − 10)/9. Check n = 2: 108.
Bar heights for AP 2, 5, 8, 11 with the common difference d=3 marked between consecutive terms.
Concept context
Arithmetic progressions, geometric progressions, and sums