The 6th term of a G.P is \(\frac{-2}{27}\) and its first term is 18. What...
MATHEMATICS
WAEC 1996
The 6th term of a G.P is \(\frac{-2}{27}\) and its first term is 18. What is the common ratio?
- A. -1/2
- B. -1/3
- C. 1/4
- D. 2
Correct Answer: B. -1/3
Explanation
a, ar, ar\(^2\), ar\(^3\), ar\(^4\), ar\(^5\)
6th term = ar\(^5\) = \(\frac{-2}{27}\)
1st term = a = 18
=> ar\(^5\)
= 18r\(^5\) =\(\frac{-2}{27}\)
r\(^5\) = \(\frac{-2}{27 * 18}\)
→ \(\frac{-1}{27 * 9}\)
r\(^5\) = \(\frac{-1}{243}\)
r = \(^5\)√[\(\frac{-1}{243}\)]
r = \(\frac{-1}{3}\)
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