Answer: 2ac/(a+c).
- A 2ac/(a+c)
- B (a+c)/2
- C √(ac)
- D (a+c)/ac
Correct answer: A. 2ac/(a+c)
Explanation: HP means 1/a, 1/b, 1/c are in AP. So 2/b = 1/a + 1/c = (a+c)/ac. Solving: b = 2ac/(a+c), the harmonic mean of a and c.
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