Question 9
Sequences and SeriesThe third and seventh terms of an exponential sequence (G.P) are 9 and 1/9 respectively. Find the first term
- A.81
- B.27
- C.9
- D.1/3
Show the answer and explanation
Answer: A (81)
Explanation
ar² = 9 and ar⁶ = 1/9, so r⁴ = 1/81 and r² = 1/9. Then a = 9 ÷ (1/9) = 81.