Answer: a/(1-r) + dr/(1-r)².
- A a/(1-r) + dr/(1-r)²
- B a/(1-r)
- C dr/(1-r)
- D a + dr/(1-r)²
Correct answer: A. a/(1-r) + dr/(1-r)²
Explanation: Let S = a + (a+d)r + (a+2d)r² +… Multiply by r: rS = ar + (a+d)r² +… Subtract: S(1−r) = a/(1−r) + dr/(1−r). So S = a/(1−r) + dr/(1−r)².
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