The 6th term of a G.P is \(\frac{-2}{27}\) and its first term is 18. What is the common ratio?
- -1/2
-
-1/3
- 1/4
- 2
- 3
The correct answer is: B
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 = \(\frac{-1}{3}\)