Answer: n+1.
- A n
- B n+1
- C n(n+1)/2
- D 2n
Correct answer: B. n+1
Explanation: Use negative binomial: 1/(1−x)² = (1−x)<sup>−2</sup> = Σ C(n+1,1) xⁿ = Σ (n+1)xⁿ. Coefficient of xⁿ is (n+1).
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